Popping sound in right speaker

sounds like a bad tube..

Yes, you probably have a bad tube. Try swapping the left and right channel tubes in your CD player first, and if the noise switches channels, you have found the problem. If that does not do it, replace the (single) 6DJ8 in your hybrid ARC LS2 pre-amp with another known-to-be-good 6DJ8 and see if the noise goes away. Of course, be sure to turn things off first and let the tubes cool off before removing.

I would also say it's a bad tube. I had almost the exact same happen to me and it was a bad preamp tube that was brand new.

Thanks for the advice regarding the tubes.