If you have more than a couple of dozen MP3 -- and let's be honest, none of here have,
then you'll need
MP3Trim. This little joy is absolutely indispensible if you want change volume levels, chop bits of silence from the start and finish of tracks and mend mangled files.
The first really cool thing is, MP3Trim does it without converting the file first and then recoding it after manipulation -- which introduces loss. MP3Trim works directly on the file and is entirely lossless.
The second really cool thing is that it's FREE! Don't hang about, just get the new version 1.85 now!