then you don't need to change the MP3, but rather the way it's being played back.
Is it really a Mono recording, or is it perhaps a Stereo recording that has the same thing on both the left and right side, but at different levels?
If it's the former then you should be experiencing a similar "offset" when listening to other things. Even most Stereo stuff is, generally, mostly coming from the middle of the speakers.
I hope this makes sense!