I Have A 1999 F350 Crew Long Bed 4x4 W/80,000 Miles, When I Am Diving In Town And Useing A Light Foot On The Fuel Feed I Get A Rumble/grinding Sound From The Back Of The Cab Area. Everything Looks Good Under The Truck. This Sound Goes A Way When I Cost Or When I Speed Up. The Carrier Bearing Was Loose So I Repaced It The U Joints Looked Good. Would This Sound Come From The Rear End?? Thanks

 

If you have a limited slip rear, you may need to add some friction modifier.

 

Thanks I Will Try That.

 

Is it a vibration and does this happen between 38-45mph? If so, I'm afraid that's a common vibration that comes with our trucks.

 

No Vibration But The Sound Happens Around 30 To 40 Mph , And Not All The Time. I Put In Some Limited Slip Additive Do You Know How Many Miles Before I See A Possible Difference?? Thanks For Your Time

 

Well The Limited Slip Additive Did Not Work. I Am Thinking Of Replacing Both U-joints Next. They Felt Ok , No Play. Any Other Ideas For Things I Should Look At?? The Sound Is At The Rear Of The Crew Cab. It Comes And Go 's Thanks