Car makes a thump noise when apply gas from a stand till

[axl266]

2007 Buick Rendezvous with 149,000 miles. So I've noticed that after driving the Buick for a while (35 miles or more) sometimes when I'm at a red light and I press the gas to go the car moves but you hear a thud noise from the back of the SUV. I know it could be a transmission slip because it kind of feels like that but it doesn't seem to be a tranny slip. If you apply the gas normal you don't have an issue. While driving the transmission works flawless. You can feel the Buick shift nice and smooth. This only happens while stomping on the gas and moving from a stand still. I checked the transmission fluid and it's bright pink and the transmission fluid level was exactly in the middle of the dipstick. This started while we drop 650 miles to Myrtle. It happen while we were driving home. It didn't happen again for like 5000 miles until just the other day. Any ideas would be great.

 

[TollKeeper]

Check the rear suspension, shocks, springs, and stabilizer links.

Also check your spare tire, if the cable is loose, it may be banging around on the frame, and sub-frame

 

[bambam]

or it could be a rear motor mount causing the exhaust to hit the firewall.