Google Chrome no longer plays certain audio files
I'm not 100% on the specifics of this, however, it looks like some MP3s using older versions of Lame, or longer than a couple of minutes, or at high (300 <) or low (128 >=) bitrates seem to be affected. It appears to be webkit-related, as it also affects Safari users.
HOWEVER!
As a solution, re-encoding the MP3 files using 160Kbps bitrate, and the latest version of LAME (3.99.5) seems to have fixed this, and they now play normally across all major browsers again.