A Question About Power-Noisy

I have had a sibilence issue for a long time and after too many equip/cable swaps im beginning to think its really power related. My conclusion is based on the fact that today i was plugging some stuff into my VH Audio hot box while the system was playing and the grunge, hash sibilence got really nasty as i plugged something in and out of the box. Unfortunately, my front end must be plugged into this box because it is basically built into my wall unit which is in turn built into the wall. Bottom line i cant change this power distributor out because of the furniture blocks access to the duplex.

OK, so im in an apt, and trapped with this power distributor. Any thoughts on possible help to tame some of the hash. Initial thought would be to try another smaller pc plugged into the hot box but the box already has some minor filtering....