Signature 600 chuffing

[Creek]

This is my first post.
ISX ReCon 600 CM570 just under 500k mile. Getting a chuffing sound at all rpms. Can hear it at idle. Gets louder of course with increased boost. Truck runs great, no power loss, good mileage, no smoke of any kind. Had a Volvo shop check the overhead. Said it was fine. Don’t really trust that opinion however. Thinking of getting it checked out again. I am in NC 45 miles NW of Charlotte. Any good shops up here? Anyone have an idea of what would be a good of course of action?
Thanks a bunch.