(if I swap the silver interconnects left to right the static remains on the left).
I would think that would rule out the cable being the problem.
What type of RCA plugs did you use?
Measure the center pin length. Is the pin length the same as other ICs?
Make sure you are pushing the RCA plugs all the way in the RCA jacks. Left channel center pin contact on the preamp or power amp jacks may not be making good contact with the RCA plug pin.
With the silver pair of ICs connected gently move the left channel RCA plug side to side and up and down on the preamp and power amp and listen for the static sound. See if you can recreate the static at will.
2. I also recently bought a pair of balanced XLR cables but when I turn the power off on my power amp, I get quite a loud popping sound from the left channel. Just can't get it to go away
Power amp should always be be turned off first. In your case you might want to wait about a minute before turning off the preamp to allow the power supply caps in the power amp to bleed off.
The fact the popping is only heard in the left channel tends to point to a problem in the left channel of the preamp or power amp.