I realize this could be totally unrelated since you seem to have pin-pointed the 430 as the source, but wanted to share an experience with breaking squelch in my plane.
Currently fly a Mooney 201 (building an RV10) and was having squelch break problems in it. It was finally traced to a USB plugged into my panel's aux. power plug (aka, cigarette lighter) that is used to power my iPad in flight. Replaced with another $10 USB plug and has not been a problem since. Google search will show USB adaptors are notorious for creating RF noise.
N783V - Reserved
Flying Mooney M20J
Emp Kit Completed, Fuse 40% done, QB Wings delivered and stored for now.
Dues Happily Paid 2018