Strange sounds...

[Geoduck]

I recently got these games from a friend (Xenosaga, Chaos Legion [Japan import], Breath of Fire V).

Whenever I use these games on my PS 2, I can hear a very soft whining noise (inaudible if I have the PC, or air-conditioning turned on) during loading and reading.

The games are used, "handed down" to me by a friend. They do have some hairline scratches, but function perfectly. The problem has nothing to do with the machine, since I tested with older games before this "whining noise" problem, and they functioned perfectly without any noise.

The bottom line:

Are these games (these DVD's anyway) bad for my PS 2 (such as causing wear on the laser)?

Could it be a matter of "unorthodox" DVD types (DVD9, DVD2)?

Should I stop running these games in my PS 2?

Thanks in advance.