As for what i've heard from others,it could be the Hard Disk SPINNING and the CoverFlow....
Make sure to have the iPod Classic to it's latest,1.0.2 version,disable ALL the CoverFlow options and EQ.
When you highlight a new song,BEFORE you select it,put the back of your iPod at ya ear and press the select button...you MUST heard the Hard Disk SPIN...if it KEEPS SPINNING ALL THE TIME press MENU 2 or 3 times slowly,then see if the HD stops spinning...if it does,great job!..if not,try opening a video and then press MENU...
Constant Hard Disk Spinning makes the batter Drain in nothing..so make sure to turn off your iPod MAKING SURE the HD is NOT spinning...then ya done.