Please help, weird noise drop when exported as mp3

I’m exporting each chapter for my audiobook (recorded as separate tracks). I had them all saved and backed up as WAV files first. They all passed the ACX check.
When I exported as .mp3, everything is fine, except that now there seems to be less than one second of silence at the beginning and end of every single track. If you string the .mp3 files together in one audacity track, as if to read through the audiobook, there’s a tiny break between each chapter now. When I listened through as a .wav file, there was no added silence.

However, when I do silence finder, it doesn’t find any silence. So maybe it’s not silence but, what is it? More of a cracking? I’m attached samples of both the WAV version and the mp3 so you can hear it.
On test mp3 you can hear 2-3 seconds in, the audio goes out a little bit, but not in the wav file. The wav file is smooth. I wanted to submit my book tonight but I know ACX wants readers to hear a seamless transition between chapters, and with the weird audio drop I suspect it’ll be an issue.

How do I fix this? Any ideas? ACX requires .mp3 format. I’m not sure why this is happening when the .wav file was the same before export…

Please help! I’m trying to finish up my first audiobook and get it uploaded ASAP.

Thanks for the help!

How much less than 1 second (approximately)? About half a second?

It is normal (unavoidable) for MP3 files to have a tiny bit of silence at the start, but it is only a few milliseconds. That is a limitation of the MP3 format.

The current “Audacity 2.4.2” automatically hides that silence for MP3s that were created in Audacity (or any other MP3 encoder that supports support the LAME Mp3 info tag).

I’m not sure what you are trying to show us with those two files. The MP3 file is shorter than the WAV file.
Do you mean that you were expecting “more” silence in the MP3 file? If so, please take us through, step by step, how you are exporting the tracks.