So, i picked up this truck at a used lot. It runs and drives as a truck should but when I get the truck up to 60 MPH I hear a whistling sound from the back. When I let off the gas it goes away instantly and when I put back on the gas it returns? Could this be a vacuum leak? Or something more serious? The truck is an automatic with the 4.7, 2wd 90K miles. It shifts smooth and I dont notice anything else wrong with it.

 

Gear whine maybe. Have you serviced the rear diff yet?

 

No not yet, Iv had the truck only a week. I didnt notice it on the test drive but I am now, just at around 60 MPH. Ill likely go to my mechanic tomorrow and get schedualed for servicing. Just wanted a heads up on if I got a lemon or not. lol That would be awful.

 

Ujoint usually are if it goes away when letting off and comes back when putting the power back to it.. Possibly exhaust leak whistling when on the gas..

 

Thinking its just an exhaust leak. It seems to do it more when its cold outside. Didnt get a chance to see the mechanic this week, ill get it serviced next week though hopefully.

 

Common issue is that the rear two bolts on the manifold break at the head causing an exhaust leak. Have him check for this.
Thankfully, the remaining bolt inside usually comes right out with a simple bolt extractor. Usually a quick and easy fix...

 

So, took it to my mechanic today, he drove it and told me its the pinion bearing, he said its SLIGHTLY off kilter (or something, I cant remember his exact words lol ) he checked the fluid and said its clean of metal so he said to just ignore it and the only way to fix it would be to replace the rear end. lol So, at least I know what it is and not to worry about it, I only drive about 10,000 miles a year IF that. So.. This should last me a little bit I hope.