Exported MP3 sounds different than previewed in Audacity

I loaded a wav file then did some editing and normalizing and previewed the sound to make sure it is what I want. then exported as MP3. But the sound of the MP3 is different than what it previewed to be in Audacity. the sound is a lot deeper and has a different sound to it as well VS what was previewed in Audacity.

Is it slower, too? Is the length of the show the same as in Audacity?
Are you listening to the show by importing the MP3 back into Audacity?

Do you know what a very low MP3 quality sounds like? When you exported the MP3, did you use the standard quality rate of 128?