Help! Strange humming sound started today

[rkrall]

My Impreza started making a strange, humming noise when I accelerate. It hums for about 5 seconds and then is quiet until I apply the gas again, but maintaining speed, idoling and stopping make no noise (at least not that I can hear). Has anyone had this happen to their car? My serpentine belt started squeaking last week and I am replacing it tomorrow - not because it's very loose or warn, just that it's wearing and at 70,000 miles I'd rather just replace it. Maybe that has something to do with this new noise? Thanks for the help!

[Fairtax4me]

What year, engine, and transmission, and how many miles on the car?

 

Can you replicate the sound by revving the engine in park or neutral?

Edited July 9, 2010 by Fairtax4me

[rkrall]

It's a 2006, automatic transmission, 2.5i engine with 70,000 miles. I can't get the sound to replicate revving the engine in park or neutral. Only makes the sound when accelerating, which is what is throwing me off....

[Fairtax4me]

Is it more apparent when the car is moving faster or slower?

 

Have you checked all fluid levels recently?

[rkrall]

I just had the car at the dealership in May for a transmission flush and other fluid levels are within range. The noise was really noticable driving slower in town. I noticed it a little twice when going over 40mph, but it's much more noticable at lower speeds.

[idosubaru]

central/left/right?

 

i've heard alternators make noises like this before. low humming mostly under load. but on a 2006 with low miles that would be weird?

it's not like a wind noise?

 

does it sound definitely engine related? would be nice to get it to rev and see if it's engine related (changes speed with engine RPM) or drivetrain related (changes speed with wheel speed so to speak).