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.
agdthree
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 SPL...as, the Citations I have tried them bridged, biamped, un-bridged...singled...same issue.
10 years later... looks like I have the same issue. Every single input change, surround change, even selecting from an Apple TV to Netflix and all I get is Pop pop pop from my 7.1 Citation. Wired same way as my Citation 22 or if I use a PA4000 no issues. I even tried my HK 990 and it’s fine. As soon as I add the 7.1 into the configuration pop pop pop. 
My set up:

Either Onkyo PRPZ 5100 or ONKYO TXRZ840 as preamp

citation 22 as center
citation 7.1 as LR bridged
PA4000 as rear and height channel 

wiring is all monster cable 
Monster AVS2000

speakers
JBL L7’s and L1’s 
or 
JBL Studio 590 and 580’s

any help would be appreciated. 
I've had the citation amp since new. When it started to age i noticed an on and off pop only.  Have used nad m, 3 different arcam processors. Worse on arcam av9, would pop every input change.  Talked to some people at local store, they thought capacitors were starting to go. Currently use arcam avr850.  I could bi amp with arcam but can't get myself to part with the citation amp 23 years later. Still love the sound and drives the my main speakers effortlessly