Rumbling sound on deceleration and at lower speed

[Nursemedic88]

I bought a new 2023 1500 5.7 etorque. Day and a half after buying I starting hearing a rumbling type sound that only happened on deceleration and more prominent at lower speeds. I’ve tried deactivating the anc and it still happens. I took it to the dealer tech had to get a star case involved, they replaced exhaust (took over a month) and it’s still there. Can anyone help!

 

[Nursemedic88]

Also have turned off MDS and have been driving when slowing down started hearing it out it in neutral and still hear it and it’s at base idle