Mar 25, 2012 03:17 pm heya djbolly, and welcome to the forum. I'm a little short on time, but I wanted to get this in so you're not left hanging or anything.
Could you give us some more details on how you mixed everything down? Such as software/DAW used, bitrates/depth/quality of the wav file, whether you dithered down from a higher to lower bitrate, was the bass track a recorded wav file, or something else, like an mp3 that got mixed down to an mp3? What is the quality/bitrate of the mp3 you compressed the wav to? Etc.
Things to keep in mind: mp3 is a lossy format, so if any track in the DAW was a lossy format such as mp3, ogg vorbis, etc. it will lose more data when it gets converted to an mp3 again. However, if everything in the DAW was either a VSTi instrument, or recorded audio, or a wav file, and it played back fine, then I don't know where things went wrong unless the mp3 is very low quality and it's killing transients or something.
Maybe some other folks have some ideas to help pinpoint where the problem is cropping up.