GD-ROM Disk Repair Question

[cheatengine]

I bought a copy of Ready 2 Rumble: Round 2 yesterday, but my DC wouldn't read it due to a small, but deep scratch on the disc. I attempted to repair it using a CD Cleaner that has fixed minor scratches on other DC discs, but this time it didn't work. So I visited my local Gamestation (UK) who have a professional disc cleaning machine and thankfully the game now works. However my laser was making a lot of noise reading the disc, with what sounded like erratic laser movements. This also happens with another disc (Sega Bass Fishing) that was professionally cleaned before I bought it.

Any idea what is causing this and is it a known issue with GD-ROMS?

Thanks in advance