In air leak can cause odd noised under various running conditions as air if forced through a orifice (think wind instruments) ...AND...unmetered air entering the engine can ALSO cause the DDE to think you are getting erroneous NOX readings and trip codes.

I would NEVER think a code that says "nox sensor" means unequivocally that the nox sensor is bad. Never. Good guess perhaps, but not the only thing that can trip codes.

my 2 cents