Creating gapless mp3's

The biggest PITA ever. I’m trying to use looping sounds in my project. Anyone have a perfect solution to this? I’ve tried using LAME’s nogap. It worked fine on a music file I made. But for some reason it won’t work on the sound I’m currently trying it on. I’ve tried --nores --nogap and other things. I don’t see why it would work for one sound and not the other. :{