Encoding issues in Linux (low volume for aac->ogg)

[yairmohr]

I've been using fre:ac for a couple years and loving it, but since I moved to Linux (Mint, if it matters) about a year ago there's been a problem interfering with my use:

I purchase music from different stores in different formats, keep them backed up and create an aggregate OGG folder of everything as my main music archive. Since moving to Linux, every new song I downloaded through iTunes encodes at an extremely low volume (The m4a files usually get to about -6dB, and the fre:ac ogg files all cap at about -18dB). It doesn't happen with older iTunes AAC files, with files of different formats or with other encoding software.

What could be the problem?