2005 Grand Prix GXP Odd clunk when engine is warm and happens over smooth and bumpy roads.

There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.

There are now two versions of the Chassis Ear. The original one has six microphones that must have wires run into the car where they plug into the receiver box. The new version has two of those and four wireless microphones. That makes setup much faster, but that model costs twice as much. If you want to see what they look like, I can look for the link from Mac Tools. Matco and Cornwell guys have them available too. If you want to buy this setup for yourself, ask at any new car dealership or most independent shops for the names of the tool truck guys and when they stop in. Most visit each shop at least once every other week, often every week. Most also don't mind if you call them at home.