I don't mean to dismiss your gear, simply volunteer my (limited) experience ...
Whenever I have tried repairing CD players (always cheap ones), I end up condemming the laser LED for being unable to focus. Everything else seems OK, just an inability to 'see' the disk. It seems to be the stock fault !
The sound you hear is interesting though, could this be the focussing coil (motor) of the laser assembly struggling to find focus with a duff LED?
I would be interested to hear if you do find the LED at fault and if you can get a replacement.
[Yes I know this is a DVD but they are just high capacity CDs !]
... right I'll shut up again now !