UK-POLOS.NET - THE VW Polo Forum

i have a mk4 polo 1.4cl, ans whenever it gets to a highish revs it sounds like the exhaust is vibrating on the bodywork , but, my mechanic has had the whole exhaust down and he says its not touching the body anywhere, he also looked inside the cat to see if that was ok and he said it looks fine,
so what the hell else can it be, its sometimes deafening. its got me stumped, i originaly thought it maybe a cheap rear box but it sounds like its coming from the front end of the car, my guess is the cat ?? what do you lot think it could be.

could be exhaust baffles rattling inside the silencer.

mine used to rattle and it was the heat shield around the exhaust middle section catching on it.

Baffles is a good start, sure it's the exhaust? Does it go away if your travelling at reasonable speed and you put it in neutral?

My girlfriend has the exact same problem, the car is fine most of the time but sometimes at motorway speeds its deafening and when you let off the throttle it gets worse. Its definately a resonance problem, I originaly thought it was the kwik fit back box and mid box so I replaced that. During the replacement I found a loose heatshield above the back box I took it off. The problem is still there, I am really stumped now, I am guessing since nothing else seems to be rubbing or loose the problem must be inside the cat. There is really no way that two different exhaust systems would have the same loose baffles. I am sure its the exhaust though, the only other thing that could make those noises would be a wheel bearing but they were all checked on the MOT, besides its done it for ages now, a bearing worn that badly would have failed by now.

defo not a wheel bearing, its wierd, as you say it only happens at a certain speed, it sounds like the the exhaust is touching the under carriage and it vibrates like hell, also i noticed today that there is a slight misfire on exceleration which is leaning me more towards the cat, i might get another 1,4 and change the exhaust from the downpipe back and see if that cures it , if not its going to auction.

Yeh i was getting a a possible wheel bearing.

Have you checked for cracks in the manifold?

No a wheel bearing makes a grinding droning sound, this is a vibration either like the exhaust rubbing against the chassis or something inside the exhaust vibrating.I would expect a cracked manifold to cause missfires and backfires and also it would be very noisy all the time.

Well I had a cracked manifold on my old car, and it was making similar noise to whats been described on here, may be worth a check

Tim_GTi wrote:Well I had a cracked manifold on my old car, and it was making similar noise to whats been described on here, may be worth a check

By jesus you were right, just whipped the heatshield off the manifold and not only was it cracked but two studs had snapped as well. Never would have thought of looking there, the old man was a mechanic for years and he hadn't thought of that either. I replaced the studs but I need to get my mate to weld or braze the manifold up, hopefully the noise will go away then!

funny you should say that as when i bought the car the was a stud missing on the manifold, so best i get my mechanic to check the manifold monday.

Glad my bad experiences with my old car helped you out!

Tim_GTi wrote:Glad my bad experiences with my old car helped you out!

Actually I am not so sure it did, I got the mani welded up but the noise was still there. I then jacked the car up and found the mid box was close to the heatshield so I moved it but still the problem didn't go away. I then did some tests and decided that the noise is speed related rather then rev related. The old man (mechanic for 30+ years) said it may well be the wheel bearing. I checked and there was a ton of play in the hub, upon inspection the outer bearing was scorched. I will fit a new and see if that solves the problem.

ahh so probably a wheel bearing after all! Hope that sorts it for you mate, I know the feeling when there's a fault and you just can't find it!