Hello and welcome to everything you'll ever need to know that's XT related..

The popping on overrun is the AIS and you'll need to disconnect the pipe. Essentially when the throttles closed the electronics open a valve via a solenoid I think that puts air into the exhaust gases so they burn off or pop/bang.

Don't play with the electronics or mechanism, just disconnect the pipe or you'll have more troubles with the ECU getting confused.

I've done this with my Ten' but you'll have to search the forum for how to with your X.

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