Prob with cd/dvd unit

[deuce]

Hi,
I got prob for a while now with cd-rs on my jap ps2 10000, they boot but then they stop at a loading time (the screen freezes).
Yesterday I dismounted my ps2 and took the cd/dvd unit out of its place, I reconnected it to the ps2 I let the unit on the table, started a cd-r and surprisingly the game at the critical moments never freezed.

So what could the prob be?