2000 Ford Explorer engine ticking noise

My 2000 Explorer w/4.0 SOHC motor broke the serpentine belt a couple of weeks ago. Before replacing belt, I checked all pulleys and everything spun freely. After replacing belt, engine makes a ticking noise at idle speeds. Noise is coming from left side of engine (tensioner, alternator area), but is only present when compressor is on. Noise goes away if compressor is off or engine goes above idle speed. Noise is also only noticeable when engine is warm-does not happen on initial start-up or even on start-up after truck has set for 10+ minutes.Talked to a Firestone mechanic and he remembered having some cutomers come in with the same problem and he sent them to Ford for the fix (as he tried replacing tensioner, alternator, etc. with no success). Any ideas?