Metallic Buzz in my TVR S1

[LoFlyer]

I have a 1988 TVR S1 that generates an annoying metallic buzz when the engine is under load at about 2,000 rpm. It's not speed dependant and doesn't happen when revving the engine in neutral. The sound seems to be coming from the center, rear of the car. I've checked and readjusted the exhaust system. I've looked for loose items around the differential. Can't find anything. It's loud, annoying and driving me nuts. Anyone have any ideas?

[phillpot]

Baffle loose in the silencer?

[magpies]

jack the back end and put on axle stands (chock the front wheels) and try in gear (each gear). If you hear the sound then have someone else in the driving seat while you CAREFULLY crawl under and see if you can hear where the noise is coming from.

[NicBowman]

Hi, I had a problem with the body mounting bolt in the centre tunnel. The rubber had disappeared leaving a bolt which rubbed directly on the body shell. Super irritating. I don’t recall exactly how I got to it, few years ago, under the centre console somewhere. I got some two part flexible epoxy and potted it in. Fixed it a treat.

[GreenV8S]

One way to track resonant noises is to just tap on panels / components and see whether any of them sound vaguely similar to what you're looking for. Components that resonate will tend to ring at a similar frequency when you tap them.

[LoFlyer]

Hmmm... good suggestions. I'll check the tunnel from the seats rearward. I'll also check the rubber mounts on the differential again. Maybe I missed something. It sounds like metal on metal. But I can't figure out why it only occurs around 2,000 rpm. If it's loose baffles in the exhaust box, that would be continuous above some engine speed. If all else fails I guess I'll put the rear on jack stands and see if I can recreate the noise and maybe track it down with the help of some friends. Quite a mystery.

[GreenV8S]

LoFlyer said:

I can't figure out why it only occurs around 2,000 rpm.

That's a typical symptom of something hitting resonance. You might find it happens again at some multiple of that speed.

[greymrj]

Be interested to hear if this diagnosis from an S1 owner is right!
It is a vibration in the oval front part of the exhaust system. It is caused by the outer case touching the perforated internal pipes. 90% certain you will find a dent in the oval outer section and as the clearance is small they touch. The sound comes at a certain revs when the inner reaches a resonance. Annoying the sound seems to be at its most intense at town traffic speeds!! Bash it a bit more and the noise will 'move' revs a bit!!

Originally the space was filled with wadding but that will have broken up and gone by now.
I am afraid the only solution is to slit the section both sides with a 1mm slitting disc, hammer out the bend, repack with the exhaust wadding* and reweld.
5 years later it may well come back but at different revs!!

(* you can get some clever wadding these days that is held tight by a 'string' while you pack it, the 'string' melts at exhaust heat and the packing swells to fill the space. Car Builder Solutions, Demon Tweeks, and others supply it)

NOTE for those who dont know this exhaust. The down pipes go into the oval front section of exhaust. That is actually an absorption silencer, and is the main part of the silencing. The box section is largely empty except for a number of baffles. These baffles can come loose and 'buzz' but the problem in the oval pipe is most common.
It is a design issue really, the system works well if undamaged! But as it is on an S it WILL get damaged, especially on an S1. The solution is expensive, a new system! One where the only silencing is in the 'box'.