Last Saturday while pulling a bay boat, I was noticing increased road noise when I wasn't in the accelerator. Anytime I was coasting there was road noise similar to when you are driving on a grooved road. I took the boat home and did a test run and the same noise. I've checked all the tires, Trans temp is 161, it doesn't sound like exhaust. Has anyone had this happen to them? I have about 8000 miles on Michelin M/S II's. Today I started to be able to hear a little of that same noise while cruising at 55, it was intermittent.

My thought/hope is that I have a tire that is separating, but I've never had this happen before. Another thought/(hope not) is rear end trouble. My wife thinks the sound is coming from rear half of vehicle, but I cannot tell.

 

I forgot to mention it is an '04 with a 6.0L.

 

Well lets start with the basics!

It is time to check the following in what ever order you want to!

1)all 4 wheel bearings. (The rear actually has 2 per hub.) Jack up the truck as you want. 1 wheel at a time is ok. Grab the wheel and try to pull it back and forth side to side and then top to bottom. If there is any movement more then a 1/32 to 1/16th it is time to replace them.

2) jack up each axle one at a time and place it on jack stands. Grab the drive shaft close to the pinion(where it attaches to the axle.) Try moving it up and down and side to side. Any movement means bad u joints or pinion bearings.

3) Check the backing plates on each axle. 1 per side. Make sure they are not rubbing the rotors. I once decided to be cute and go over parking stops and a flower bed to get to a parking spot that was open. A juniper bush pushed one into a rotor!

4) it is possible that it is tire noise. When was the last time you had the tires rotated and balanced?

It is possible that you have bearings going bad on the ring gear carrier! The only way I know to check that is to pull the covers and pry up on the ring gear and then on the side. any movement would be a bad thing. You should see metal in the diff fluid if that is the case.

 

If it only happens when coasting, especially with tow haul on, and especially if is or starts to be accompanied be a vibration, it's probably the u joint.
That's exactly what mine did.

 

I've had this happen before. Turned out to be a pinion bearing. Only on coast.... would be quiet when I put foot on accelerator. I hope this isn't the case for you, it is expensive to have repaired unless you have the tools and knowledge to set up a ring and pinion.

Good luck!