so i have a 6505+ stack and im running various rack and pedals through it,

but whenever i switch from clean to heavy i get this loud POP

explain please? it obv can't be very good for my amp

Gibson SG faded, black hardware/ EMG81-89
peavey 6505+
GMajor Effects Processor
BBE 362 sonic maximizer
THD Hotplate
Avatar 2x12 w/ Hellatone 60/ K100
Behringer FB1010