I recently put my a/c belt on my car and ever since then I've heard a squeaking sound coming from the hood of my car. Before the belt initially snapped the tensioner used to come loose all the time and cause a horrible screeching sound when running the a/c until i tightened it, Which i attached a picture of. Recently the squeak got worse and when I step on the gas it turns into a loud screeching sound until it stops at about 45-50 mph. I tightened that square screw in the attachment hoping that would do the trick like usual but to no advantage. Any ideas anyone? sorry for the long post and thanks in advance.

Somthing not spinning frealy maybe.

The belt should be pretty tight though

I had an itching noise too . The tensioner, pulley, belts replaced . Tensioner was main reason . Before changint these parts I squirted WD40 it was gone for a few months and came back later .
I also had a problem with the fans , that was relatively an easy job but that noise was not bearable . In this case I had to replace a main unit that attaches two fans one for main and the other for auxhilary fan .

Sounds like that "square nut" adjuster is not doing what it should, maybe the lock bolt is not locking the assembly once the adjustment is done????.

OR, the plastic idler bearing has siezed and needs replacing.

OR, the other belt is squealing.

OR, the vulcanising of the front pulley is parting company with its parent centre piece.

OR, the a/c compressor is siezing and causing whatever you do to squeal.

Some quiet investigating is required, eliminating on item at a time.