Reading issue

[Dustpuppy]

I have a discovered a little thing latley.
My ps2 reads backups cd-r, DVD-r just fine, also original ps2 games.
but if I pu in a original dvd movie and start up then it will go so far that I start to see the electrons before the screen go black and show "PLAY" in upper right corner.
Ok, the elecrons only shows up, don't so long that they start to swirl.

but as I said, with all my dvd-r and original ps2 it starts as fast as it should.

any suggestions why it only effects the original dvd movies?
a dvd movie backuped on dvd-r starts as it should. so it seems like it struggles abit to read the original discs...