Laser problem, please help.

just got a ps2, I only tried ps2 games and dvds,
with ps2 games, it loads fine and in a reasonable time (around 13-15 sec), game video play fine and haven't seen any skip (I tried the GateWay), but after about 20 mins play, the DVD-ROM starts to click for several sec and back to normal, and after a while starts to click again. it just repeat like this.

So what's the problem with it? can it be solved by adjust azimuth or replace laser or something else?

Many thanks

BTW, the ps2 is not chipped at all.

What model, new or second hand?

if new - return. If second hand - return if possible.

do the games load fine / play fine still whilst this clicking is happening?

www.cyber-mag.com/station/laser.html#sectC