hum noise from front of vehicle.

[MikeWoodBooks]

After some recent mechanical work, I have been getting an occasional noise from the front of the vehicle. sometimes it seems like its the right front, sometimes the left front and sometimes the middle. The noise initially sounded like that of a finger circling the inside of a glass. the noise only lasts one to three seconds. It occurs during acceleration, deceleration, steady speed and when parked. It might happen ten times in a ten mile drive, then won't happen for the next couple days. It only seems to occur when the AC is on. Although one time I shut the AC off shortly before I parked the car, and when I pulled in to park it started making the humming noise.
The work I had done was: front rotors resurfaced and new brake pads installed. A/C recharged and hoses replaced, full tune-up and oil change, and the right front CV axle shaft replaced. I took it back to the repair shop. they thought some gunk in the throttle body was making the noise. they cleaned that out but it did not cure the problem
Any ideas? thanks

[timgluntz]

I had my turbocharger on my 2005 Baja replaced in March. Since then on occasion I hear a noise that sounds like a fog horn that only lasts for a few seconds. It maybe the sound that you are hearing. It seems to occur when it is hot and I am using my AC. Did you have any hoses replaced or work done to your engine? My mechanic says he has heard noises like I described and they turned out to be a faulty bearing somewhere. I am really stymied and am starting to get concerned. I really want to find out before it becomes $$$.

[MikeWoodBooks]

they replaced the AC hoses but that did not solve the problem. it's been a while now, but what i think eventually solved the problem was replacing the AC compressor. the whole situation was just discusting in that we replaced a lot of different parts before finally solving the problem. I eventually decided there were just too many reliability issues for me and sold the car.