The AC was not working and my husband turned it on to see if it would mask the sound now the ac is working. He thinks maybe something broke loose and that is what is making the noise. Would that happen even when you don't have the AC running? By saying sounds like a bus it is sounding like a diesel engine when its not
The A/C compressor will not function unless the hub on the front end is engaged or stuck and turning as the engine turns, otherwise the only thing turning on the compressor would be the pulley, and that should turn at all times as the engine runs.