big thump while downshifting

[goober544]

hey
i have a 1993 Grand Am SE automatic
when i slow down or come to a halt, as soon as i downshift into first gear i believe
(when i drop below 20 MPH) i can feel a good thump when it downshifts
granted this is nto a big deal, as ive had the car for 2 years and its always done it, but if anyone knows why it does this and what can be doen to possibly fix it, thatd be awesome
thanks
~justin

[Ridenour]

Try having your tranny fluid drained / filled, and your filter changed. Especially if this has never been done.

[goober544]

I have already had the fluid drained and replaced a while back, as well as had the filter replaced. any other ideas?