50 CAL - Those cables are unbalanced. You might want to try some 1/4 inch to XLR balanced cables. Your KRK accept XLR or 1/4 inch. Balanced cables are supposed to be better and cut down on noise and popping when turning monitors on/off. They worked for me. With unbalanced cables my monitors would pop really loud when I shut them off. Now they don't, so I guess it's true.
I don't know about that so I can't say, but a good power conditioner should eliminate most AC hum and RF interference. Also, you should never run speaker cables parallel to power lines, this will cause AC hum. Any of these equipment stores have all kinds of gadgets and filters to block out all types off noise, hum and feedback. Some cheap and some really expensive. If you invested any money in gear, a few more bucks for a power conditioner is good
insurance.