Pull the little carpet tabs behind the rear seats, then pull the foam cushions, and remove the upper shock nut (be careful to secure the shock tower itself from spinning, it can damage the shock internally - I use a locking grip on the top part of the shock tower (unthreaded, of course) while using an open ended wrench on the nut). When you pull the upper bushing, make note of the shock tower's location within the hole in the body, and whether it's sleeved by the lower bushing. There could be metal-to-metal contact here, and that's what would cause your squeak at ANY sort of suspension movement, however minute.
1987 Trans Am GTA A4
1998 Trans Am WS6 M6
1978 Trans Am 400 A3
1978 Trans Am 400 W72/WS6 4-speed
2006 Dodge Charger R/T Daytona (#59 of 200 Canadian)