Vibration sound at 3k rpm.

[bmw.maniac 1]

On my '88 318i I seem to have a horrible vibration sound at 3k rpm exactly. When you accelerate, it sounds alright until just past 3k rpm (around 3100rpm), where it makes that sound for about one second, and then sound normal right to redline. It sort of sound like a rattling, I was wondering if it was anything to do with the exhaust mounts? I was flicking through the old reciepts the other day, and I notice that just before I bought it there was a leaking seal at the rear of the gearbox that required the exhaust to be removed. Could it be that the mechanic meerly didn't tighten up a bolt enough?

Also, i've just remembered that when driving through town sitting on exactly 2,000 rpm for an extended period of time, it makes the same noise but with a slower vibration sound. The car is not physically vibrating at all either times, it just sounds like something is vibrating.

Thanks

[*Glenn* 854]

It could be a loose baffle in one of the mufflers or the exhaust bracket on the back of the gearbox

[QuickSilver 0]

Sounds like you prop shaft is slightly out, it will do exactly what you describe (mine did anyway). They are two piece and need to be fitted together correctly to balance. Your centre bearing can cause this too, and your centre bearing hangar as well.

Edited October 1, 2008 by QuickSilver

[*Glenn* 854]

Sounds like you prop shaft is slightly out, it will do exactly what you describe (mine did anyway). They are two piece and need to be fitted together correctly to balance. Your centre bearing can cause this too, and your centre bearing hangar as well.

That would give you a physical vibration and you would feel it. He only hears the vibration, which would probably be the exhaust from his explanation.

[QuickSilver 0]

Ahh true, that makes sense,

[williams 0]

if your car has aircon check the compressor and pipes,would cause a vibrating noise in engine bay