Dedicated Lines - Problem

Well, they could be dedicated and the noise in the line is merely backing all the way back to the panel and into the main power feed, and then going back down into the dedicated circuits. Did they put any sort of noise filter on the dedicated lines at the breaker? If not, this is what will happen.

(FYI: This is one reason why your stereo typically will sound better late at night, as all of your neighbors quit using their noisy appliances late at night, and the main power feed is quieter.)

But then again, imagine how bad it would be without dedicated lines at all.

Also, what gauge wire did they use for the dedicated circuits?

Kurt has made an excellent point. Check the gauge and an industrial noise filter might make sense.
P.S.: You might check on Audiogon here. Someone has reported on his set up specific to your problem some while back. Sadly I don't remember who it was.

Thanks for the suggestions. I will do a bit of research regarding the noise filter.

Kurt tank is right. The reason for the 'POP' could be that your panel is at max current draw. Add to that maybe some older motors that generate electrical noise. Another thing to think about when adding Dedicated lines is to 'balance' the load. What I mean by that is most homes have 2 phase power coming into the panel. Phase a and phase b. Now if the A/C - dehumidifier - refrigerator - toaster etc (follow me - high current devices especially electric motors) are on 1 phase along with your system there could be some very dramatic sags surges and spikes when those appliances turn on and off.

Did the 'popping' happen before the new circuits? If not you may want to have the breakers put on the other phase. Otherwise I might think about getting the motors and starting caps for the A/C and dehumidifier checked out.