Humming noise in cabin / 2005 Tacoma

My son has a 2005 Tacoma LB 4WD with 178/K miles on it. Runs great but we've noticed a humming type sound during cold start ups in the cabin. It usually goes away once the truck warms up after a few minutes. The sound is very similar to the humming sound in the old car stereo speakers back in the 80's!

I had a mechanic listen for it during a servicing and he couldn't locate it. He said he recalls something about an "air intake" that makes this noise but he wasn't 100%.

Has anyone experienced something similar?

Thanks,
Greg

 

Cant advise if electrical or otherwise, but the "air intake" sound is from the foam lining around the air intake where it enters the fender under the hood deteriorating generating a vibration that resonates into the cab. Sounds like a rough idle. Easy fix. Two bolts, remove the old foam and apply new weather stripping that matches.

 

I have a vibration sound as well in my '06. However, it is always there and seems to be coming from under the hood somewhere. Drives me nuts as I can't locate it