OK....before you go spending lots of cash chasing down suspension noise, check the plastic compartments behind the rear seats!!! Mine had become loose and they mimicked a suspension problem to a Tee!!! Its worse when the cold makes the plastic more rigid. If you can rock the boxes for and aft, they're loose. There are 4 bolts that become visible once you remove the rear cover and spare tire cover. You can also test this theory by releasing a rear seat and then sandwiching a folded towel between the seatback and the boxes.

 

Have someone else drive your car for the first 5-10 mins lol

 

My HHR would squeak when I drove it after startup. This was particularly bad during cold weather. The sound would go away after warm up.
The problem was worn out lower control arms. I had them replaced and the noise stopped. The car had over 110K on it so this may not help the owner of a lower mileage car.

Dennis
Houston

 

I’m going to leave this one with the 13 year old thread as it is pertaining to the original cold start noises.