This sounds like a phasing problem where the audio is following two paths through the system and the clock on one path is running slightly by about 1/120Hz faster than the other.

well....i'm at no point sending it out through two directions. older versions of cubase like that require you use one card at a time. but, a conflict is something i can test for by disabling the cards. it's worth a shot. i think anything is at this point. but, i'm not putting too much faith in it.

i think the idea of the clock being off some other way is maybe a possible explanation, though. thanks for that as a path to explore.