2006 M45 Sport: Loud "thunk" under heavy acceleration

[Grantbo]

Hi all,

1 yr owner owner of a 2006 M45 and newly registered poster to this forum.

My car exhibits a very odd sound that I hope the collective here can shed some light on. Under heavy acceleration, a very loud and concerning "thunk(s)" eminates from the chasis. It not unlike the thunk you'd expect when a 19' with 45 series hit a large pot hole, but there's no pot holes. It's almost as if the shock rebound/dampning becomes overwhelmed by the weight transfer and the car slams against the bump stops....very odd. Otherwise the rides great considering the low profiles. The car has the OE shocks/struts and has 30k on the clock.The dealer seemed uninterested and wrote it off as the differential locking -up. I'm not buying it, as the sound can come from the front wheel area as well as the rear. This type of sound is never a good thing.

Thanks for any input.Grant

[exbmwdude]

Are you hitting any bumps when this sound occurs? The M rear suspension doesn't like to handle bumps and heavy acceleration at the same time and I've gotten some bad sounds out of it when hitting a bump with my right foot to the floor. That's "just the way it is" and you're not likely to get a dealer to fix this.

exbmwdude2006 M35S

[Grantbo]

Yes, the loud "thunk" only occurs on bumpy roads. But it only occurs under heavy acceleration from a standstill or slow roll. The same bumps taken at speed result in no "thunk".

"exbmwdude"...small world...I moved to the M45 from a M3 sedan.

It's a product of the suspension, but I can't determine exactly what. Poorly designed suspension I suspect. Perhaps the aftermarket will address the issue.

Grant

[Double E]

Are you certain that the spare, jack and wrench equipment is/are secured?

Can another person drive with you as you seek out the area of the interior where the sound can be heard best and better described?

For example ...is there a metal to metal sound description available or is it more like a component that's at the end of designed travel and hitting a limit or "stop" bushing?

Does it matter if theres a full tank of fuel or not? Full of people or not?

Does the same road and same acceleration conditions make it happen every time or does it not matter what road?

I realize that you shouldn't HAVE to put so much effort into diagnosing it yourself but you're the best person to do it and have vested interest in a solution

[infinitiandbeyond]

You need to see a doc about that thunk in your trunk

HAHA