That's not a common problem.
Just because a few people on a couple of websites may have experienced it that doesn't make it a common problem when you look at how many HHRs are sold. If like half of all HHRs sold had the same issue then I would call it a common problem. I would guess it's your brake rotors causing your problem. Most of us will agree that the factory HHR rotors suck and are prone to warp easily. It think mine lasted about 15,000 from brand new before they needed turning and they were warped again by 30,000. I ordered EBC rotors to replace the factory crap rotors but they haven't arrived yet.