Jake brake noise when letting off the gas

sierra2014

I just bought a 2014 GMC Sierra SLE and quickly noticed when im going at least 30mph and let off of the gas it has this loud jake brake type of noise that sounds like it's coming from the front to middle of the truck. The dealership can't get the truck in the shop for 2 weeks so im trying to figure out what the issue may be before then.
5.3 has a cold air intake, dual flowmaster exhaust 4x4
Again it only happens when letting off of the gas, if i brake there's no noise, sitting idle no noise and no noise when accelerating

kyfdx

Not an expert, but that sound might be related to your aftermarket exhaust system.

J9D

What if you dont have an after market exhaust system? VW Tiguan 2013, same thing 🤷🏼‍♀️

J9D

Its my heat shield