squeak at highway speeds

Son has a ’03 Frontier with 4cyl engine that we are getting a strange noise.
Almost exclusively at highway speeds (>55) and with the air conditioning on he occasionally get a noise that sounds like you’ve stepped on the cat’s tail. I wouldn’t think that it would be that the belt is loose – thinking that it might be the a/c clutch sticking momentarily. Anyone else had any experience with this?

Any help would be appreciated.

Thanks,
Duane