I can assure you that the nitwit at the AutoZone is wrong, it is not a faulty A/C compressor clutch.
I would suspect a shorted PCM power relay or a faulty ignition switch.
Something is providing power to that relay when it shouldn't. If your mechanic has the EVTM and understands how the circuit works, he should have no problem locating the source of the stray voltage (unless it's due to a faulty wiring harness, then all bets are off).
You can do some more diagnostic work before taking it in.
One at a time, pull the WOT relay, PCM Power relay, F3, and F4 from the underhood fusebox. Let me know which, if any, stop the buzzing upon removal.
Steve
