2012 silverado crew cab 5.3 Z71. bought used 73000 miles. Has odd rear end double thump or thud at braking... It will do it 100% of the time at slow speed braking hard pretty much only going forward. Off and on it will make same single thump sound taking off slow. I've taken it to two different chevy dealers who had no luck fixing. They greased drive shaft, re-tighten leaf spring, said it was a baffle in the gas tank and was due to a 1/2 full tank and would go away at full tank...which of course it didn't change. issues is getting worse and I am going to get rid it if there's not a fix...but there has to be a fix. Other than that I really like the truck. I've looked online and on youtube. It's no the common shifty in and out of gear noise. When braking hard it thump when truck rocking forward then again when it rocks back. HELP PLEASE

 

Wouldn’t hurt too much to have the rear differential cover pulled and have the gears and bearings inspected. Braking changes the loading on the axles.

SD

 

My 2013 started to make a thumping sound on take off. I was lucky it was still under warranty. The dealer replaced the input bearing in the differential and the transmission mount. No more thump.