The alternator on my 2003 F150 Crew Cab is making a whining/moaning noise when it is damp or foggy out....I was wondering if it will hurt anything if I leave it..seems to be charging alright!!
Does anyone know what could be the problem so that I could fix it (ie regulator malfuntioning)???
Thanks for your help

 

Could just be the berring, I would go a head and swap it out or have it rebulit. The berring could lock up. Pull the belt off and spin the pully and see if its grinding.

 

Pulled the belt off spun pulley..and no noise.....very queit!!!

 

Many times the problem is the tensioner pulley and not the alt pulley bearing. But with that said, just spinning the alt pulley isn't enough to tell the tail. It's not under a load or as fast as operating speed. In most areas there are shops the rebuild alternators for under $100. They will usually give it a look to help you diagnose the issue. That's much better than waiting for it to fail and force you to spend money when you don't want to.