Silverfox

I have 2 brand new 2011 1LT HHR's and both have the same rear noise.
So after doing some serious looking around I have found the problem and the fix.
This may or may not be an issue on earlier models but I got 2 in a row.
When going over a sudden bump from whatever source, I got a low pitch knocking noise in the rear of the vehicles like something lightly banging together.

After looking high and low I discovered that the lower rear bumper plastic facia that encloses the Tail pipe exit could be easily be moved up and down.
It is fastened with plastic fastners to plastic brackets, one on each side of the car.
I surmised that when I hit a fairly sharp sudden bump that this facia could be quickly nudged up, and then drop back down to the resting position.
It could be just one side or the other, or both.
The fix I used was not to try to find a solid fastening point as that isn't easy to do and might not even be needed.
Instead I took a piece of 3M self adhesing Non Skid material and cut it 5" long by 1" wide. I peeled the stick side paper off and then doubled it back over the other side to stick it together making it 2 1/2" long when finished and the non skid surface on both sides.
I then took one side at a time and wedged the material between the bracket and the plastic partition that the bracket is fastened to.

That was enough to tightened up the loose connection making it solid enough to stop the movement without a substatial tug to get it to move.
This material is inert and the weather and water conditions will not harm it.
It can't rust either. It non metalic so no noises emmited.

Took out and tested today and WALLA.....Noise completely gone.

You should be able to buy the 1" wide 3M material from some Auto or Marine stores. Comes on a roll that they will cut to length. Comes in Gray or Black.


3M: 3M™ Safety-Walk™ Medium Resilient Slip-Resistant Surfacing
Series 300 - Rubberized, Suitable for Bare Feet


DescriptionSpecs
Features
DocumentsSafety-Walk Medium Duty Slip-Resistant Surfacing has a textured polymer surface that offers both traction enhancement and resilient characteristics. It is generally used on smooth, flat barefoot or deck shoe areas such as decks, docks, showers and recreation rooms. Best for light and medium traffic areas. Available in a variety of sizes including custom sizes.
• High friction, medium⁄coarse rubberized surface
• Reverse surface is coated with a pressure sensitive adhesive covered by a removable protective liner

Black 1" X 60ft. roll 3M part number 19293
Gray 1" X 60ft. roll 3M part number 19321

Be sure you are looking at the right product as 3M makes several different types of Non Skid Material. This one does not have the sand like non skid finish.

HipHotRod

I used nuts and bolts - took the cover off to mount the crush piece to the rear beam rather than the inside of the bumper cover. When I put it all back together I used nuts and bolts where those useless black clips are. These cars are SUPER noisey.

THE BATMAN

Gonna try it tonite .

Silverfox

I thought it might be just me that felt the HHR is kinda full of strange noises at different speeds and conditions.
Mine are both fairly tight but do have some unwanted noises...
Such as wind noise comming from the center of the dash area ??? Weird...
I am going to do a few tests to see if I can get a handle on that one.
Dealers go nuts with wind noise. To time consuming.
It's in both new 2011's so I don't know if older models have it too.

Tire noise can also be an issue depending on the hiway surface condition. My Firestone Assymetric OEM tires go from relatively quite to ultra noisy and even start a drumming noise in the rear on some blacktop roads. Kinda like the rear window open buffeting issue.
That noise is not there on my other HHR with Michelin X Ice tires I just put on.

If Chevrolet would have kept the HHR in production and made all the fixes needed they would be able to sell a new one to most every current owner.
It's a great classy small car but full of inconsistant issues.