[E36 G]

Hi folks,
I have a 1997 318ti with about 154k mi.
About 2 weeks ago, when the temperatures just started dipping to about freezing in the early morning, the car now makes a very loud creaking noise from the rear hatch/rear suspension, rear something or other.

Symptoms:
Car creaks from rear when going over bumps, big or small, going slow or fast. The creak sounds like rubbing of broken plastic interior panels or sheet metal rub (sounds like noise is more inside the car than outside). ONLY Happens when COLD. After 10-20 min of driving, the noise goes away!?!?!

- Troubleshooting:
1. I cannot make the noise appear by pushing down, lifting up, or 'yawing' the rear end in anyway when car is stationary.
2. Cannot get the rear hatch to make this noise in the up or down positions or even when shaking the hatch door in my hands violently. Rear hatch closes very solid and when inspecting: no detectable movement of the hatch occurs relative to the car once it is shut.
2. I've taken apart all the plastics enshrouding the rear light assemblies and side storage cubby holes in the trunk and have found no indications of rubbing/damage/wear/broken parts.
3. creaks the same with rear seats up or down.

Car Details:
In the past 20-30k miles the car has received NEW everything in the rear (and front for that matter):
-trailing arm bushings, new
-shock mounts, new
-shocks, new
-subframe bushings, new
-sway bar end links, new
-brake discs and pads, new
-brake fluid flush, new
-exhaust hangers (both on the resonator), new
-tires, new
-rear hatch support strut (only pass side new, driver's side hatch support strut is still the old one)
-rear diff fluid, new
-OEM clutch for the tranny.
-driveline feels as tight/loose as historically.

-car still drives just like before, rear hand brake, etc...all seem normal in operation...only the rear end creaks now!?!?

Any help would be much appreciated.
Thanks!