The problem is the white piece (made of plastic) is touching the axis of the motor (made of metal)
Everytime the motor moves there is a friction in between the piece of plastic versus the piece of metal... and you can imagine what is going to happen in long term
The white piece have 2 "dents" that wears out and becomes roundy, this creates a gap and reading problems
When the wear out is too much the white piece even does "jumps" on top of the motor axis, at that point we could say that the white plastic piece is like "toothless" and this is what causes the annoying sounds
There is no way to fix the white piece, you need to buy another one (or recycle it from a dead laser)... but remember, when you replace it you need to:
1) Clean the old lube very well from the motor axis
2) Use solid vaseline to lube them (easy to find in tubes in a drugstore)
*this detail about lubing them with vaseline could look a bit uneeded, but it helps a lot