Not enough info given by you.

1 Which PS and country of origin
2 Is the symptom confined to one type of game, e.g. NTSC

Where I'm heading is that e.g. on an NTSC PS2, a PAL game might jerk around unless patched for NTSC or unless you've got a NTSC-PAL convertor in line for these games. Reverse for a PAL PS2 but same principle