by "RPM" you mean the sansamp rackmount preamp? all i can contribute is that gig to gig my shure PSM700 box sits sometimes on the floor next to my amp, or next to the pedals for my mandolin, sometimes near my bass pedalboard, and i've never noticed the slightest bit of interference one way or the other. in my other band the bass player's PSM600 box sits in the main PA rack along with the mixer and all the EQs and comps and stuff, and there's never been an issue there either.
To add.. my old L6 G90 and now my Senn D1 have both sat in the rack on top of whatever amp I was running.. which for a couple of years now has been and SVT7Pro. Zero interference from that config. Our IEM wireless units sit in the same rack as our X32 Rack, and a snake splitter. Again, no issues. We also run a dual band router for remote IEM and FOH control.. again.. no interference... but I do configure the router to minimize any of that.
