howling under the hood

[Esel]

After refilling (probably overfilling) my A/C, I started hearing a howling noise from the engine. This was weeks ago. The howling would start once the car warmed up. Tapping on the accelerator would stop or start it. I felt all the auxiliary belt pulleys, feel fine, and changed out the belt tensioner. Noise is still there. I've driven quite a few miles like that.
Because I was too dumb to check on the forums earlier, I started changing out my bad radiator. Now I came across the PVC SUMP CLOG NOISE posts. Can't pull the dipstick to see if that's it. My buddy still thinks it is the A/C compressor. To me, the noise sounds like it's caused by moving air. And I couldn't pinpoint the source. The Volvo has 130,000 miles on it. 1997 850 GLT.

[abscate]

You can easily troubleshoot the AC compressor by getting the noise to start, then turning it off with the switch.
Other candidates

PS pump
Alternator bearing
Serpentine belt tensioner

Timing belt components - WARNING - will kill car if it fails.

Finally the oil thermostat on these cars is known to moan when it gets old.