This squeak has driven me crazy for years. I've had it in a couple of GM dealerships and we can definitely reproduce the squeak but could never find it. After some searching online someone else posted a solution and I have altered their solution somewhat.

The squeak is caused by the rear e-brake cable rubbing on a clamp that affixes it to the rear lower control arm.

The fix: remove your rear tires and locate the e-brake cable (runs from the front of the car to the calipers). Look at the rotor and on the driver's side, the clamp is in about the 10:00 position (2:00 on the passenger side). Use a screwdriver to open up the clamp and create clearance between it and the fitting that is pressed on the cable. Lube both parts with Never-Seize. Here is where I have altered my solution: In my opinion, there should be a nylon bushing here, GM should never have made this metal on metal! I don't have ready access to nylon bushings so I cut a 7/8" length of cheap vinyl garden hose and inserted it between the cable and the inside of the clamp. I then used a pair of pump pliers to squeeze the clamp closed tight to hold the new "bushing" and cable in place. The result? NO MORE SQUEAK! I was ready to drive this car in the river and now I can drive in peace again.

My 2006 Pontiac use to make a very noticeable whine noise in the front end when taking sharp turns, over slight bumps, hills, speed bumps, whatever! The solution to this very ANNOYING problem is the rubber boot that's over the strut is what causes the noises. To eliminate the noise simply remove the rubber boot completely or take some Automotive Anti-Seize lube any auto parts store sells it and apply to the rubber boot housing were the boot meets with the end of the strut housing. The noise will bother you no more!!

Update from Sep 24, 2010: Hello everyone I finially found out the problem to the anoying front end wine, squeak sound that we all know and love (I say that with complete sarcasm). Its from the front suspension and the cause of the noise is a 3 ring rubber crown looking peice that is around the strut under the rubber strut boot. Remove the rubber strut boot and you will see this rubber peice around the sliver shiny strut cut, or remove it you dont need it on there anyway and I kid you not that noise will bother you no more. What caused the noise when the strut would go up and down over bumps this rubber ring would go up and down rubber on the strut causing the wine squeak sound!

Attention all Pontiac G-6 Owners. When driving your car do you get a very annoying loud squeak noise coming from the rear suspension area when driving over speed bumps or on any rough road surfaces? I figured out the simple solution to this thanks to the Pontiac g-6 owners club website! For me it was not any suspension part problems it may differ for others! The simple fix I DID IT MYSELF is there is a brake cable on both REAR sides that has a metal clip that is screwed onto a part of the rear suspension, just take some never seize mercantile and coat the clip that is screwed to the suspension. The noise will magically disappear, I kid you not! The noise is from the metal clip rubbing on the suspension part that moves up and down when driving the car. You can fix it yourself just jack up the car remove the REAR tires and the clip is from looking at the brake rotors at a 2'oclock position on the back RIGHT tire and at a 10'oclock position on the back LEFT is were the clip is above from the rotor!!

Update from Aug 30, 2010: The front strut boots is what Causes the sharp wine noise coming from the front end of your G6. I tried cutting down a small amount of the rubber boot to prevent any rubbing interference it really did not help cause the noise comes from both top and bottom. A stupid thing like this makes such a horrable noise why it does it is beyond me. Either cut the entire boot it should remove noise but then the strut itself is exposed or a temp fix is use lubercant. The rear of the car has the struts go into the body of the car so there is no need for a boot if only the front of the car was like this AUGH !