Mouse squeak from rear accelerate/decelerate weight transfer?

Senna-F1

2014 Nismo 11K miles. Short tails, Swift springs, SPC camber arms and toe bolts. Hotchkis swaybars. This didn't happen right after installing any of the above. I am getting a huge amount of squeaking from the swaybars or endlinks, but this is different.

During dive & squat, as in accelerating and decelerating, I get ONE quick SQUEAK from the rear. Loudest in 1st gear, lower volume in 2nd, lower again in 3rd due to I assume less movement and transfer. Dont hear while just driving down the road or going over bumps. I removed my entire trunk contents, panels, tools, foam, tire, sub, and the sound simply got louder, along with the exhaust. So, I'm pretty sure its coming from outside, underneath the car. I've lubed swaybars, torqued swaybar brackets, and all other bolts related to the suspension... endlinks, toe bolts, camber arms and bolts. Have NOT removed and reseated rear springs yet. Again, they've been fine since I installed them a few thousand miles ago. Stock struts, so I never removed those.

Any idea what would only squeak during dive/squat in the rear?