Single Thump When Slowing

Hi!



I have a '98 Saturn SL1 with an automatic transmission and 145,000 miles on it. I am mostly car illiterate but not afraid to learn and get my hands dirty.



In the summer time while slowing down I hear a single loud thump and feel a jerk. It sounds as though it’s coming from the back of the car. I believe it may only happen when the AC is on. Also, I’ve slowed to under 15-20 miles an hour when it occurs.



Any idea what this could be? Or anything else I should check?



Thanks!

Chad

cv joints?