i was using a peavey vmp2 with two mics for about a year with no problems

then tried just one mic, u87 in omni, into the vmp2 into a masterlink. the
other cable was left in the vmp with no mic connected, input volume turned
down to 0. strangely there was level on the channel with no microphone. the
miced channel had more level though. both channels sounded messed up on
playback as if there was no phantom power being supplied, crackly on peaks.

wondering what can cause these problems

i disconnected the input cable to the vmp with no mic, and disconnected the
input to the masterlink from the unused channel. this fixed the problem.
only one channel on playback and it sounds fine.