I've had that an a GTA3 original. We've sort of solved it in a number of ways and in this sequence:

1 We laid the PS2 horizontal. The Read errors stopped but FMV skip remained

2 We cleaned the lens with a flail DVD but FMV skip remained

3 We borrowed a little used PS2 - no problems whatsoever

4 We sent the original PS2 off for attention. Comes back friday