If the drive belt is at correct tension and has a bit of belt dressing applied, it will not make noise. A dying pulley bearing my give intermittent noise/squeal - the idler or the compressor in this case. Try using a stethoscope applied as closely as possible to the bearing housing to detect rumble/rattle indicating incipient failure.
I don't try to use a medical type scope in such cases - use one with a straight rod (someone makes/sells them) BUT the best for me is one I have made - a small can with a long rod through the bottom (thin welding rod?) - tip of rod on the moving part and can cupped to the ear. Easy to hear internal noises and bearing noise will be apparent..
If you heard the squeal from inside the vehicle, it could be a fan motor noise - including a squeal - sometimes happens only on start-up.
