1991 Chevy Suburban Ringing noise

I have a ringing noise(like small bell) coming from the bottom of the vehicle when I drive. It is sort of embarrasing as it sounds like an ice cream truck coming down the road. I have looked at every square inch of the bottom of the Suburban to see if anything is loose and can't find anything. I don't think it's the U-joints as they make a squeaking sound when they are dry, but the noise does seem to come from the rear end.