could be two things I know of....
slow clicking... tick tick tick... usually is the laser trying to focus on the disc... that sound is the lens moving to the boundery of its coil....
a grinding set of clicks... tit tit tit tit tit... the laser's sled (or slide as some call it) is not lining up with the worm gear... this will try to push the sled in towards the spindle and beyond it's track... forcing the gears to skip as it is...
I've noticed that if you open an older machine up and mess with the sled.. it will work for a while again... then start acting up.... although in my experience only a few times loading games before f'ing up again.
I'm not sure what can be done about it... If you can get replacement parts then you might be golden
PS3 Slim 320GB
PS2 v11 exploit w/300GB Maxtor
PS2 v10 exploit w/80GB Samsung - Network Games
PS2 v10 exploit w/60GB Samsung - Network Games
PSP 1001 3.52M33 w/10GB total storage
NDS DSReal 4GB