grinding noise when i let off the gas

[cameronmcclure]

Hi guys i have been noticing that when i am running down the highway faster than 55 and let off the gas my truck has a grinding noise until i get under about 58. If i am running faster than 65 it won't start doing it until i get under 65. While cruising no matter the speed it doesn't do it and the truck runs great. I haven't lost any power. To me it sounds like the tow/ haul is on. But its not. Just wondering if anyone has had similar issues. It does not affect the way the truck runs at the moment i am just making it sure its not cause for alarm. Thanks.