I get a gunshot sound when I change patches

This sound is a built in part of the tape delay plugin in MainStage that happens when the tempo is changed.

You can either make sure the delay is turned down before changing patches, or create a dummy(duplicate) patch of your next patch that doesn’t have a tempo change so the initial effect isn’t changed. 

If you can make sure the patch after it has the same tempo, then you shouldn't get that noise.