Exhaust brake making noise more than usual

[elm]

I thought it was an exhaust leak looked around and found the pipe where the coupling is had some soot on it so i replaced the coupling , it seemed to quit the noise down, But wheni went to take it for a drive there was no noise until i switched the exhaust brake on and there it was again.
any help would be great.
holiday rambler 40pdq 400 engine, cummins