Here is a weird one. The wife told me about a strange noise from her 94 S Blazer. She said it sounded like a motor driven siren turning real slow. It only does it once in a great while and only after going uphill and cresting the top. So I took it out today and finally it made the same noise. Running about 45 when it started, tossed it in neutral and no change, put it in 4 wheel and no change, shut down the engine with no change, hit the brakes and still no change except as the truck slowed the noise slowed as well, once it got below about 10 the trucked made a little jerk and the noise went away, it didn't come back. I looked for any rubbing and nothing.
I THINK it may be the right rear axle bearing but every one I have ever heard just seemed to rumble never this kind of noise. Anyone have an idea?