I drove the truck last Sunday and noticed that whenever I took my foot off the gas I noticed a very slight "humming sound". As soon as I go back in throttle it goes away..... I was out of town for a couple of day and on Tuesday my wife says that she hears the sound now and it's getting louder. On Wednesday while on my way home I get a panicked call that it is now 'super loud humming / groaning'. I test drove it today and confirmed. Seems worst when doing about 40 MPH. As soon as I go back on throttle it totally goes away. I gave it a look and nothing is visually out of place, nothing rubbing, and I'm pretty confidant it is not an exhaust leak or the exhaust rubbing on anything. Sounds like under the hood... maybe back pressure related?
Truck drives and 'feels' totally normal with the exception of the sound. Of course, the B2B warranty just expired. Any ideas?