2007 R56; Standard hatchback; Automatic; 118,000 miles.

For past six weeks there has been a noise coming from under the hood, possibly from lower part of motor or transmission.

The noise is present only when car is in gear and accelerating.

Noise is a low-frequency buzzing that matches the engine RPM -- that is -- as I start from stop, the noise increases, then, as transmission shifts, noise drops back then starts rising, etc., all the way to top gear when it stops. If I lighten up on the gas, noise recedes then stops. If I am in top gear and accelerate do not hear it.

No indication in gauges, no fluids leaking on the cement garage floor. No impact on performance; noise is not always present -- about 60% of the time.

Please don't tell me I need to tear down or replace transmission.

Thanks.

 

Is it possible it's the timing chain? I have read that timing chain replacement is advised around 100,000 - 120,000 -- I'm at 118,000.

And how much does timing chain replacement cost?

 

First off the cuff guess is the torque arm on the low side of the engine. If you have OE one, replace it with the newer one.