Howling from cab
 

I am new to this site, so far i am very impressed just doing some searches and seeing the great answers. Anyway on to my problem. I recently purchased a 1999 Silverado 1500 with the 5.3L Engine. Truck has about 154K runs great shifts perfect and 2H,4H and 4L all work great. My problem is, after about 25 MPH i get a howling sound that's coming straight from the cab. Doesn't sound like its coming from the rear or the front but right underneath me. Now the sound will only resonate while im on the accelerator if i let off the accelerator the sound goes away and if the tranny downshifts as i slow down and puts force back on the drivetrain the sound comes back. Iv been through a few things, iv changed the tranny fluid and filter. Also changed the fluid in the Diff and the Transfer case which the fluid in the Transfer case was extremely low however there was no metallic swirl in the fluid or chunks of metal. Like i was saying everything works great the howl is just so lowed it almost overpowers the radio. Any help or ideas would be greatly appreciated. Thanks!

have you ever check to see if its actualy out of 4x4??? get under and try turning the front driveshaft.. it should turn freely........ only other thing is maybe a tire..but then again you said it was under the cab.. i had a tire start howling a year or so back.. becuase of uneven wear.. oh and welcome to the forum!

Support the rear end on jack stands and run it. If it goes away look at the front drive system. If its still there maybe you can locate it. I dont think this has a two peice drive shaft but if it does suspect the brng in the center. Also noise can travel up a hollow drive shaft.