HK Citation 7.1 & 5.1 "pop" when turning on or off

I just upgraded my receiver (which I use the preouts) to the new Onkyo TX-NR5007. I know, a lot of you guys feel it's a sacrilege to use a receiver as a pre-amp...but it's a good value and has a lot of inputs I feel.

So, I have the pre-outs feeding a bridged Citation 5.1 for my two center channels (Infinity Kappas), another feeding a Citation 7.1 which I use to to biamp the L/R Kappa towers and another Citation 7.1 feeding the SR/SB channels.

Recently the wife has noticed a high pitched pop when starting up, turning off, and sometimes when switching sources or THX/DTS modes.

I'm wondering if it's the old solid state amps charging up down and that's the joy of older tech. If I've got a ground loop problem. Or if there's some solution.
I would start by cleaning all your RCA plug connections.
Does the pop happen on all speakers? If so, start at the receiver or preamp. You might also try swapping IC's out too, just remember to power down first.

I have a Citation 7.1 and there are relays to control power up/down, so very unlikely it's the problem.
It does happen on all 8 speakers (not the sub).

I tried using a few different ground loop hum eliminators from the preamp/receiver to each amp, but that added more constant noise in the background.

I'll try some deoxit. I'm using bluejeans cable interconnects, but will try another brand and/or roll my own.

I do have all three amps rackmounted, at the base of my rack, with a couple inches on the top/bottom. Any chance they are interfering with each other?

I also have tried hooking them up direct to a dedicated outlet and to a Panamax conditioner.

Could another component in the chain be adding noise? I had a groundloop issue with my PS3...HDMI can pass on noise...but I fixed that....could an old analog tape deck or some other component cause the popping?

I used Axiom's Coax in line ground loop fixes for my Tivo 3 and cable modem...which is how I got the PS3 to behave.

Look forward to your thoughts. Thanks again.
Ok, tried de-oxit, swapped cables, and unplugged everything from the receiver. Still popping at shut down, turn on, and when I switch some sources and/or decoding mode (e.g. THX games vs PLII vs DD).

Is it possible that the pops are simply coming from the receiver (which I'm using pre-outs on)?

When I hook up a Sunfire out, the pops are way less pronounced, still there, but I attribute that to the newer "soft start" of the Sunfire and the potentially less, the Citations I have tried them bridged, biamped, un-bridged...singled...same issue.