PS2 slim, playing direct through a non-HDTV through the component (RCA) input.
The only game I have is GT4.

When playing back, occasionally the screen will appear jagged horizontally; it looks like interlacing artifacts. This comes and goes throughout a race. It's not too bad, and it most noticable on the minimap and other on-screen display.

Any ideas?

I have this on my GT4 no matter what TV it's watched on. It would seem that the programmers have pushed the machine to it's limits and it's simply struggling to refresh/fill the screen. It's not a fault, just a programming/machine quirk.
Yours,
mab.

Dude, thanks SO MUCH for the reply!!! I can breathe a sigh of relief now that I know neither my 36" Sony nor my secondhand slim PS2 are on the fritz.

Happy racing-
K