As the title states I have a front end knock that goes away in 15-20 minutes driving. The noise is a 'hollow knock' that is different from any usual noise associated with the front end going over bumps on city streets. I did some searching and the most suggestions are "anti sway bar bushings". I don't understand how that can be with the noise disappearing after 15 to 20 minutes driving on city streets. It only makes the noise when I hit a bump. The noise seems to be coming from the passenger side. My HHR is a 2009 LS with 58kmiles. There is no vibration, shake or shimmy associated with the noise. Nothing felt in the steering wheel either. I also read that bumper panels might cause a noise but dismissed this because the noise goes away(as stated) every time. It is almost like something has to heat up and then the noise disappears??? I don't mind doing searches but in every instance of my searches no one mentioned the 'knock or noise' going away after a short time only to reappear the next morning. I checked with Chevrolet and the bushing are only $7.15 each so I am going to try that. Worst case is I can eliminate that from the list of suspects creating the noise.

 

Instead of dismissing you could just go ahead and look. Jack it up use a flashlight.

I can't think of anything specific that would go away after warming up, but it could be anything that expands with heat.

 

I'm guessing maybe a strut (not any of the mounts or bearings) but the strut cartridge itself ?
My thinking is maybe the strut has to get "pumped up" so to speak before the noise goes away. The fluid internally then leaks down after it sits overnight.

Like stated, just guessing.

 

I guess X-2

It's side specific and makes some sense.

With 58K it would not be a disaster if that were not it.

I would also Replace both sides and any other associated parts needed.

SF

 

It might be that the noise stops after some movement and the lubricant gets spread around the part like a swaybar end link or a swaybar bushing, I'd inspect the rear LCA bushings also, but then again I'm kinda OCD went these noises crop up.
The wife says down boy, stop ordering all those parts and get out there and check it out! Then she has a cold wobbley pop for me when I'm finished!

 

Well I checked the sway bar bushings and they are in good shape. Glad it wasn't them since it appears you have to drop the frame to change them. Checked all the front end parts and nothing loose or showing any indication of a problem. The strut has less than 10k miles on it as does the axle on that side. Now there could be a problem INSIDE the strut, not visible.
I remember nylon tires used to bump and make noise when cold. Could it possibly be the tire? My tires are Mastercraft, not high dollar tires but still pretty good tires. This is my 4th set on various vehicles without any problem. But....just asking.

 

No, you don't have to drop the frame to change the sway bar bushings.

Try swapping the tires around to see if the noise moves.

 

Just keep in mind that if you switch your right front tire to the left front, it will be rotating in the opposite direction.
If you just move the right rear to the right front it will be a more accurate test.

I doubt your tires have nylon but an off brand ?? who knows. It should be on the outside of the casing showing you the cord materials.

Only causing a problem on one of 4 of the same Brand tires would more likely indicate some kind of defect if it is in fact a tire.

SF

 

Make sure you properly torque those lug nuts, 100 ft lbs. NO impact guns!

 

From the 1st post: "It only makes the noise when I hit a bump. The noise seems to be coming from the passenger side. "
Based on this, I would have to eliminate a tire as the cause.