Hello, The fan normally will get louder when you are running a backup & the drive is asking to be cooled.  If you here the fans ramping up when the TL is idle & not doing any backups then it could be a possible air flow problem.  Also what you can do to ensure that the fans are running at the correct speeds is to upgrade the firmware on the TL.  Here is a link to get the latest firmware:  Let us know how it goes
Get a ramped up noise from the fans as if they are going into a higher speed. It lasts for a short period of time then the library quiets down again. The only other time I hear this sound is during initial power up of the tape library. Wondering if this is normal? What causes the higher speed of the fans? Sign of need of maintenance of the unit even though ther are no error codes or lights? If maintenance nees to be done what needs to be looked at?
Increased high speed fan noise from PowerVault TL2000