iTunes wants to figure out the song volume stuff for its Sound Check feature, which you can disable in the Playback tab of Preferences. However, the Determining Song Volume madness persists if that is part of the Burn settings, only available when you are burning a playlist to CD (or pretending to):
1) click on any playlist.
2) click on "burn disc" (bottom right) - a pop-up window with burn settings will appear.
3) untick the "sound check" box.
4) click "burn" (just leave the disc drive empty, you dont actually need to burn a cd).
5) up the top, itunes will ask you to "please insert a blank disc" - just click the x and close this message.
6) click "burn disc" again to view the pop-up window - you will notice that the sound check box is now unticked. (click burn or cancel to close it)
7) close itunes, give it a minute, then open it again and you'll notice the problem is fixed!
Source (and thanks!)