Carbon fiber bike + trainer...noticing flex when tightening trainer....

First of all, you are using the skewer that came with the trainer right? This is a steel skewer, most that comes with wheels will be aluminum, which is too soft for the trainer and will deform and flex.

You will have some flex when you clamp down on the frame, this is normal, but it shouldn't be a whole lot flex in the rear triangle from the clamping force. With the correct skewer, you shouldn't need a whole lot of clamping force to keep the bike stable.

Yeah, using the trainer skewer.  It's hard to notice, but I think there is some flex.  To be honest, it's hard to tell if it's the bike moving laterally as I'm tightening or if its the bike triangle flexing.  

I will say, when I tighten the skewer, I'm pretty sure there is some (small) flex.  That's normal too?

But I'm not sure why there would be flex tightening the trainer (after already having a tight skewer on there)...but I think I noticed some.  The trainer is definitely only screwing on the skewer and assuming the skewer doesn't flex, I don't really know how it could be compressed.  Could it be the hub/bearing?  Or maybe I didn't tighten the skewer tight enough and I'm noticing that become tightened...?  Or maybe it's just my eyes seeing the bike move sideways as I tighten...