Air Conditioner Noise

Could be an entirely different component, (especially if the A/C is working) I would start by looking at the idler and tensioner pulleys, when the A/C engages it puts a big load on all the other accessory pulleys and tensioners, if one of those is marginal it can make noise.
Pull the belt OFF and check for excessive play or roughness in the bearings while spinning the pulleys by hand.

 

Low refrigerant charge will not cause high head pressure. If the charge is low and the head is high, something else is wrong, most likely a restriction.

 

Did you ever find the cause of this problem I've been reading through the thread because I'm having the same problem but can't seem to find the answer.

 

Did you read all of post #18 on page 1. Is your situation anything like this?

 

Yeah but there was no resolution in his post it ended with a new compressor on the truck but the noise still occurred and it not being the alternator.