Reply to technics 1200 tempo/power question

hey guys, i'm new to turntables/DVS and would like your help with something i've noticed on my decks.

if i have turntable A playing, it holds true with little fluctuation (.01 bpm and stuff)
if i stop that and play turntable B, same again. both with strong timecode signal.

if i have both playing together - they both pulse up and down about 5bpm every second.

i have them plugged in to the s4. both TTs and the S4 are running on their own power strip.


also, its been really hot in my apartment the last few days, so i don't know if it is my laptop slowly suffering (it was regularly reaching peak in traktor) but the pulses were happening to both tt's at the same time, and they were just fine if only one was running... also, it didn't make a difference if the 'tempo reset to zero' button on the tt's was enabled or not.

they are both technics 1200 m3ds with shure m447s... running an older mbp with traktor 2.6.1.

ideas?