TwoPedal

For a few months now, my car has made an odd whirring noise from the rear. The sound is pulsing and happens as soon as the engine starts. Its most noticeable outside the car at idle but in the quiet of the garage, I can hear it inside as well (but not while moving).

I'm sure its not the SLS air compressor so that brought me to thinking: a) fuel pump b) transfer case
145k miles and normal idle, operation, and fuel economy. Oil consumption is quite low.

I have noticed that movement can be jerky going up hill in a low gear and sometimes when turning while accelerating. Has anyone experienced something similar?

rice_rocket88

Just throwing it out there.. maybe it's simply the cooling fan for your amplifier.. I noticed it years ago in my garage when I never heard it before.. gave me a chuckle.

TwoPedal

Hmm, I never thought of that. Is the amp back there in the wheel-well of doom?

rice_rocket88

Not sure about the e61, but on my e60 the amp is actually on the driver's side, but there is another cooling fan sound on the passenger side as well.. Both make slightly different noises... They will both run after the car is turned off if warm enough just go and check