Ford explorer 1996

I have a 4.0 2wd auto explorer with 107k on it. I recently had the entire a/c replaced, along with the auto belt tensioner. Now, a very loud intermittent squeal appears to coming from the engine compartment, near the fly wheel area. Of course when i take it in to the able mechanic, no noise. It was manifesting shortly after warm up driving, then gone. It jsut started appearing intermittently postwarm up. Spacer in torque converter? The alternator is fine. Any ideas? thx!