Cant get rid of isolated hum... poste...

Hey all,

I have a hum only in my monitors that I can "move" and cant get rid of. Let me explain:

At our church we are have 2-front speakers(physical path - right main output on sound board to eq, to amp #1 to speakers, xlr cables all the way), 2 rear speakers (physical path - left main output on soundboard to eq to amp #1 to speakers xlr cables all the way) and 2 monitors (physical path - to aux 1 send on soundboard to amp #2 to speakers via 1/4" trs to xlr connector and xlr cable)

When i say i can "move" the hum, I can swap the aux 1 send and left main connections at the board and then the hum moves from the monitors to the rear speakers.

I have tried the following:

~Used a different cable from amp 2 to monitor- buzz still there
~Changed 1/4" trs to xlr connector to 1/4" trs to xlr 12" jumper cable- buzz still there
~hooked monitor speaker to left main output to verify not a speaker problem. - buzz went away.
~hooked rear speakers (originally left main output) to aux send (still going through eq and amp 1)- buzz appears.
~hooked rear speakers to aux send 2, same eq, same amp #1- same buzz
~hooked monitors through aux send 4 - no buzz.

In doing this i have ruled out, in mind, the following possible errors:

~not an amp grounding issue b/c i can duplicate buzz in rear speakers on a completely different setup and amp.
~not a speaker issue b/c i can make the buzz come and go with different changes.
~not a cable issue b/c i can make the buzz come and go with different cables as well as the same cables.

the only thing i can think of is it is an aux send problem, but the odds of two aux sends being bad is very slim.

any suggestions??

thanks