Chances are its the disc brake calipers on the front. I had this for over 2 yrs, complained to the dealer 3 times in 2 yrs and they could never find anything wrong. So it was really bugging me last week and I called to have them look again. Over the 4th week end I decided to hand wash the wheels, lots of black brake dust. While cleaning I happened to hit the caliper with a brush and it made noise. So I grabbed hold with 2 fingers and I could move the disc brake claiper laterally enough to make a clunking sound. I went and tried the pass side one and it made a little noise too but the drivers said was the worst. Went for a test drive on a rough brick surface road and when the rattle started, I lightly pressed on the brake pedal and the noise went away, lift the foot and it came back.
So armed with this, yesterday I asked the SM and a tech who was to look at car weather the calipers should move back and forth and make a clunking noise? Both said no! Well mine do I said and I took them over and showed how I could reach into the wheel and make the noise. They checked it out and agree there was a problem and they found a service bulletin on it, parts ordered.
My CTS is a early 2005 with 25,000 summer miles. Problems been there for a least the last 10,000 miles. BTW-They assured me this was not a safety issue and I could continue to drive while the parts were ordered.
Had the same issue on my 03 CTS, Mine just started happening about the 60k mile mark (out of warranty), but got worse up until a few months ago when i finally got it resolved. Mentioned it to the dealer at an oil change,but nothing was found. I also noticed that whenever i hit the brakes while driving on a rough road the sound was suppressed dramatically. My local mechanic said a bolt was missing from the caliper when he changed out my shocks/struts. How nice it is to be rattle free !!!
