19 replies to this topic

[krazynayba]

Hi all,

 

I've been having a strange sound come from the bottom of my '03 AUDM B4 and was hoping someone could point me in the right direction. I've taken it to the mechanic and i didn't have a chance to properly describe it. He took it for a drive and said he could hear the cat rattling a bit. He chucked it up on the hoist and gave the cat a bit of a bang, I could hear the rattling but it didn't sound like the same sound I've been hearing. This lead me to believe that he was hearing an entirely different sound. I thought that perhaps this was the underlying issue anyway so I didn't really object. I have a list of my findings below for analysis 

 

What does it sound like?

It sounds like a short, hollow "tink" sound. Not unlike what you would hear if you flicked a wide pipe made from thin metal.

 

Where is it coming from?

It seems to come from underneath the car, somewhere under the driver's seat. I can feel the split second vibration caused by it on the accelerator/brake.

 

How often does it occur?

It is just a single sound that occurs, then may not occur again anywhere from another second, to another few minutes, to potentially an hour or so (next time I drive the car). It is not a continuous sound that happens relative to speed/revs.

 

When does it occur?

This problem is very inconsistent as sometimes I won't hear it again for days, but it seems to be affected by the cold. I've noticed lately that as it's been very cold/rainy in Adelaide it has been occurring much more often. Once the engine has warmed up it doesn't seem to happen quite as frequently and the noise it makes when it does is quieter. Sometimes after it's warmed up the sound stops all together. I have also noticed it happen when the car was off - I had turned it off for probably 15-20 mins then got in and I heard it before I'd even started the car.

 

I'm not well versed in diagnosing mechanical issues, but I'm wondering if bits of broken cat are occasionally arranging themselves in a way which restricts the airflow through the exhaust (near under the seat) causing a pressure buildup. The sound I am hearing could be this pressure build up releasing, causing the hollow tink sound in the exhaust. This could also be affected by the outside air temperature and engine temps. Not sure if this situation is even possible but it's the only thing I could come up with given the symptoms.

 

TL;DR - Car periodically making hollow "tink" sound underneath drivers seat area. Happens more in colder weather and when engine not warmed up.

 

Look forward to hearing some theories

[Adam]

Have you run over any small children lately??

Sounds like a heat shield to me.

[Jberg89]

When the car is stationary and off. Hop in the driver seat shut the door and get a mate to gently rock/shake car. If you hear it, potentially something is loose, that would account for the inconsistent nature of the noise. I don't know here just an idea to start the process of elimination. Do you think though its only related to exhaust temperature variables?

[Morgan]

Could be the cat.

 

Mate of Jake's and mine had a similar noise and after replacing the cat, it was gone.

[Sic'Em]

From what you have described, I would assume it's something to do with heat... that most likely being the exhaust system and/or exhaust shields.

 

When metal heats up, it expands, when it cools, it shrinks again, sometimes if your exhaust flanges and/or bolts are not properly secured/tight or such, it will sound a "tink" or a "crackle" sound when either heating up or cooling (metal movement), so that would be my guess.

 

Make sure your bolts are all tight on the exhaust and the shields (take it to an exhaust place to be 100% certain), as you will most likely blow out an exhaust gasket in the process if you just ignore it (it happened to me).

 

*EDIT, on another note, if your catalytic converter inside is toast, then it will also crumble/dislodge (not sure about the "tink" noise though) and will indeed block your exhaust, hence your motor will run rough... or not at all.

[krazynayba]

Thanks for the suggestions guys!

 

I've tried shaking the car and the mechanic had a good look around/shake of stuff underneath it but couldn't hear it. Guess it might be worth doing when it's colder though just to be sure..

 

Wish it wasn't raining so much in SA atm (or I had a garage), then I'd probably just take a look at bolts etc. myself. As It does seem to come from the exhaust area, I might try to describe the issue to my local exhaust guy and see if I can organize a new cat in the process. Wouldn't want anything to go wrong with the car, and really wanna have it all fixed up before I go for a tune in the near future!

[krazynayba]

Getting the cat replaced today, fingers crossed the noise goes away! If not it looks like it's time to start checking for loose bolts!

[krazynayba]

Sorry to bump an old thread guys, but I have a little more information to go on now

I've discovered that the sound happens either when the engine is running, or when it is off and the key is in accessory. I've yet to hear the sound when the keys are out of the ignition. I was at the drive in not long ago and had to run the car every now and then to get the A/C to clear the fog on the windscreen. A few minutes after switching the engine off, and only having it in accessory, I heard the blasted noise again! This has happened on a couple of other occasions too.

 

This leads me to believe that the problem would likely be electrical. Also, I've noticed it definitely does sound like the horn of the car - When picking my younger brother up it happened as I was driving towards him and he thought I'd beeped the horn. It sounds as if somehow it is coming on for a fraction of a second, so the noise doesn't sound like a "full" horn noise. I tried to see if there was a fuse for the horn so I could rip it out temporarily (I know, not exactly legal ). This way I'd be able to know for sure if it is the horn because at least that would narrow something down. Couldn't seem to find one, but if anyone has another suggestion to break the circuit then please let me know

 

If anyone has any ideas then I'd be happy to hear them! 

 

Thanks

[Jimbo]

Has it got a Brandt alarm in it with the little keypad?

[duncanm]

wiring for the horn shorting to something occasionally ?

[krazynayba]

Hmm.. I don't know if it'd be the internal screamer as it is definitely coming from outside the car (sounds like underneath?) I'm certain of this because it does sound much louder outside the car, to the point where I've frightened pedestrians inadvertently! 

 

It does have the brandt alarm with the keypad, but as far as I know it has been disabled by one of the previous owners. Perhaps it wasn't done correctly and they've left an electrical problem behind? The central locking and immobilizer still work though, and the keypad still flashes but is unresponsive when buttons are pressed (which hopefully is enough of a theft deterrent ) 

 

I think this is the most likely case, I'm reasonably handy when it comes to electronics so I might end up taking a look at it myself. Since I'm just about certain that the problem isn't mechanical it's probably worth a look. It's quite an annoying problem as it is quite intermittent; Chances are if I went to an auto elec/mechanic they may not even hear it. That being said, lately it seems to be quite frequent so perhaps it's worth it? Anyway, I'll try and find the horn wiring diagram and see if I can trace the source of the potential short. After that hopefully it's just a matter of cleaning contacts/resoldering something

 

Thanks for the suggestions guys! If anyone has any more then feel free to shout em out!

[krazynayba]

Update - I have found a way to (somewhat) consistently replicate the sound!

 

I blew the fuse for my parking lights (because some smart fellow decided not to turn the lights off when changing the bulb ) so I had to search for the fuse. There wasn't a specific fuse for "park lights" so I took them all out and checked them, including the fuses and relays under the hood (in the end it was a fuse under the dash, one for the rear lights i think). Whilst doing this, I noticed that after I took out either "Horn Relay" or "Hazard Horn" and replaced it the sound occurred. The short horn noise can be heard the moment the fuse/relay is slotted into the socket.

 

So, this indicates that there is definitely something wrong with the horn/wiring setup. The Brandt alarm has been disabled, so perhaps in the process someone has borked something? If anyone has any method to check the horn/wiring for problems then feel free to leave a post

 

Cheers!

 

TL;DR:

• Can replicate noise by removing then replacing either "Hazard Horn" fuse or "Horn Relay" relay.
• Something must be wrong with the horn/wiring.

[Tim.]

Could be the relay itself. Have you tried replacing them with new ones and seeing if your sound is still occurring?

[krazynayba]

Well the fuse is fine but I guess the horn relay could be stuffed. I'll see if I can get another one and give it a shot Thanks!

[duncanm]

Check if anything else is wired to the cold/steering horn button side of the horn relay.

Factory cruise power is wired to it - may have been used as a convenient steering column power source for something else

[Mosti]

My b4 had this sound. Got under the car knocked around on the exhaust and found it was coming from the resonator. Knocked it a few more times, heard something fall to the bottom of the resonator and roll around abit (sounded like a bolt) haven't heard the sound since haha

[krazynayba]

Hmm well it does have cruise control hooked up but not working. It was hooked up since I've had the car but the problem started a long time after. I know it is definitely the horn. It is much more likely to occur when the weather is cooler too. I doubt it's a loose ground moving around or something, as the sound often occurs just when I turn the key from acc to off. I've taken a picture of the horn relay and I'm gonna order a replacement then see if that helps. Have relays been known to be "finicky" in a way that would cause this? Or is it usually a car of them either "working" or "not working"? Either way I'll give it a shot! Thanks again for the help guys, keep it coming!

[duncanm]

try unplugging the CC relay and see if it goes away.

[krazynayba]

Unfortunately I don't think there is a CC relay (at least not in the under-the-hood fusebox). The guy who sold it to me said it was aftermarket and it looks to be just that. Gonna try getting a new relay and replacing the current one to see if it helps. Failing that it looks like an auto-elec job, which brings me to my next question - Anyone know any good, honest auto elecs in SA?