My GX also has the 'thumping' noise/feel in the transmission/brakes/driveshaft? Actually, it started out as more of a 'skip' or 'hop' feeling in the brake pedal at about 5,000 miles. At 15,000 miles, it now feels like I'm being hit in the rear end when the brake is fully depressed. I've had it to the dealership 3 times for the same problem, only being able to duplicate it the last time. The service manager told me I was feeling the transmission downshift and it's normal. I've started to check message boards to see what others have to say, and see I'm not the only one with this problem. Does anyone know if the car actually moves when this happens? Being inside the car I can't tell if it actually moves or if it just feels like it does. It's very unnerving. Now at a light, I find myself stopping well behind the line as I feel like it might shoot me into the intersection or worse, run over a pedestrian. I recently had the air pressure sensing system malfunction and that's my next repair. Only 10 months old and I'm starting to really 'dislike' this vehicle.