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Chevy makes a grind

I have a 2004 chevy silverado 2500HD with 109,500 miles. Recently I have discovered that when I am coasting, especially down hill, at higher speeds (55mph+) a random grinding noise occurs. Sometimes this happens and sometimes it doesn’t. It’s loud and fierce, coming from the middle of the truck. Transfer case??? The ONLY way I can get this noise to stop, is if I feather the gas pedal. The slightest increase in throttle stops the noise. I’m so lost. Any ideas?

The noise might be coming from a binding slip yoke for the rear driveshaft at the transmission.

Remove the rear driveshaft, and slather the slip yoke with moly grease and reinstall the driveshaft to see if that gets rid of the noise.

Tester

slather…is that a mechaical term and isnt there a grease zirk on the shaft? Could it b slack inside the transfer case. Sounds like noise occurs when there is no pressure on driveline

http://www.yourdictionary.com/slather

Tester

Interesting… Thank you so much for your input! I’ll give it a try.

That is exactly correct. When I even brake hard or coast uphill (if that makes any sense…) it won’t make the noise. Only when it’s down hill with no pressure on the drivetrain. Slack in the transfer case? Solution?