On exhaust, do you have aftermarket or rk mufflers, my first thought is they are leaking at the clamp and you are getting a decel pop
The helmet may need some foam panned out to recess the speakers, pull back the liner and you could try a forstner bit the size and take a little out, recess your speakers and pull the liner back in.
Is the horn factory?? Most change out with a bad boy or steibel.