Why do my speakers "POP" when I turn off preamp?

HI. Is there any way I can get rid of that loud POP sound though my speakers that I get when I turn off the preamp (and leave the amp on)? My preamp is a C-J PV10A, which is recommended to turn off when not in use, but my amp is the C-J MF-2200, which is SS and can be left on. That sound can't be good for the speakers.