Not sure if it will cause harm or not, but this is what I've found out.
The one thing that I have noticed is that the "newer" high speed capable media (32x-40x) tends to be louder when playing than the older slower speed media (1x-16x)...
I burn all my cd backups at 4X....(even though I can burn at 32X)
The ones on the 32X media are noticeably "louder"
The ones on the 16X media are very quiet..
Even with both of the above being burned at 4X....
Try getting some slower speed media and see if that makes the humming go away...
It did for mine...