My 2001 Suburban is making a high pitched squeaking sound only when in motion. It started in October, I took it in thinking it was the brakes or alternator maybe, but both checked fine. The mechanic is a personal friend and I really trust his opinion, but he is swamped right now and hasn't been able to figure out the issue. At first it was only at higher speeds, 60+ now it does it all the time. But it doesn't if its parked and I push on the throttle. I'm thinking something with a bearing? Thanks!!

 

My 99 Silverado did the same thing. It had a 2 piece driveshaft and the bearing that held the 2 driveshafts where they connected to the frame was bad.