Guitar processor noise...? BZZZZZZ!

Late to the table on this, but you can try cleaning the jack on the bass by spraying De-Oxit on the cable jack and working it in and out of the bass jack. I didn't see it before; but ground path should be present from sleeve terminal on jack, to the back of each pot, ( the pickup(s) will normally have a ground wire / shield soldered to each pot, too), pickup switch, and to bridge. Some manufacturers use shielding paint in the electronics cavity and have a ground wire attached to the wood through the paint. Some use shielding on the back of the pickguard, to combat this noise / hum. I don't know about a polarity switch on the back of amps, but there is often a ground lift, and the RP155 may have one too. Like Ironracer, I too, have been jamming since the early eighties; but unlike Ironracer, though I've been in a couple good rock bands, never wrote anything note-worthy.