Once I have driven over 40 m.p.h. my 1999 Jeep Grand Cherokee begins to emit the highest pitched tone imaginable. It only stops when I accelerate. It is definitely controlled by stepping on the gas only. I took it to the shop today and they changed the serpentine belt and tension mechanism, $300!! IT STILL SCREAMS AT ME! My brother-in-law says it could be my fluid or vibration damper. PLEASE HELP! I CAN STILL HEAR IT!! ITS HAUNTING ME!!
Sounds like a dry bearing. Did they replace both idlers, or just the one with the tensioner? Did you take it back and ask the shop to fix the noise since you already paid for it?
I believe they only replaced the one with the tensioner. I took it back today and rode with the mechanic to get the car to make the noise. It is starting to be more unpredictable. When we heard the noise he would stop and pop the engine. Sometimes it would stop when he stopped the car other times it wouldn’t. You can control the tone of the squeal when you press the accelerator. He thought it might have something to do with the vacuum system, however he was unsure. So I decided to go home and do more investigating. Thanks for the reply.
i assure you that he didn’t pop the “engine” popped the “hood” 
I went to a new mechanic who actually did research to find the problem. There was a hole in the intake manifold. It is fixed and all is well. Thanks for the helpful ideas!
A hole in the intake manifold?
Really?
Did your mechanic offer any theories as to how you wound up with a hole in the intake manifold?