humming noise under hood

[q45huntsville]

I have this high pitch humming noise coming from under my hood. seems like it could be the alternator. Anyone familiar with a high pitch noise. this is a 97 Q45.

Thanks,
Ronnie

[OwnerCS]

Can you loosen your alternator belt and then spin the alternator shaft by hand? During some maintenance I found my bearings a little on the noisy side when I turned it by hand. The alternator was working fine. I picked up a Nissan rebuilt alternator and replaced it before trouble had a chance to happen.