How many HHR's have been produced with Vibrating, Rattling Rear Plastic Panels because of the fasteners???
I am on my 8th HHR and everyone has had the problem to some degree.
I am so tired of trying to fix them in desperation I decided to try a couple of different ideas I thought of.

1. Buy some 40-60lb. Braided Nylon fishing line.

a. Find the loose Plastic Rivet/Fastener allowing the movement.
b. Check each one to see how much of a gap between the head and the panel.
c. Wrap the line around the head between the panel and head to tighten it.
3-6 wraps depending on gap size.

4. Make a couple half hitches in the line and tighten them snug.
5. Trim excess material.
6. Result is a tight fastener and it does not have to be extremely tight to stop the noise. Just enough to stop the movement over rough roads.

2. I have also used small black plastic wire ties 3"-4" long.
You just wedge them in and tighten till there snug. Trim excess.

Both fixes are weather proof as well.

I used this method on my latest purchase and so far so good ......

Just another Tool in your bag of tricks.

Silverfox

 

Another option is to remove the offending fastener and take it to your local NAPA store and match it up to a new fastener. They have a book of actual fasteners "Balkamp", my local NAPA stocks most of them, but the other stores should have "Dorman" in the back room. The are NOT on the sales floor.

IIRC, there are 3 or 4 different plastic fasteners used on the HHR; My local NAPA has all of them 10 to the bag for less than $10.

 

I like using the '2 piece' type that Mopar uses. Like a wall anchor, push in the 1st pin & then push in the 2nd part, it spreads the 1st split pin & grabs really well, & are re-usable.

Got mine at Adv Auto parts.