Thanks for the screenshot and the detailed description of your problem. We could reproduce the problem on our side by trying some combinations of wave files with different sample rates. We realized that there is a problem in the uTool when re-sampling from some frequencies.
In the meantime until we get the fix done in the uTool, here is what you can do to prevent the problem:
1. Make sure all your wav files inside a multitrack song are of the same sampling rate. If they are not, please use a standard DAW to convert them.
2. When exporting from uTool, make sure that re-sampling is not taking place. For example if all the files are 48K you should choose 48K sampling rate when editing the song.
Because of the seriousness of the issue, I have made a sticky on the forum. Thanks again for pointing out this bug, we will try to get it fixed in the next revision of uTool.
Hope this helps.