Audio crackling and missing for few seconds when export

Recently I have the same problem in two different computers, a Mac Pro and a MacBook Pro.

After finishing my editing for long or short videos, when I click "share" and export my work on a H.264 format or Apple Devices or other exporting formats, at the moment of finishing and QuickTime opens my video, it begins with a crackling sound and the first seconds has no sound from the "music" line. Some other times, the music at the middle of the video just stops sounding and comes again few seconds later.

The only solution I have come with, is to delete the exported file and re-export... Some times it takes me several times until it works fine...

Anyone with this problem as well or any solution? I have look into different places but without any possible solution or even, the same problem.

Please help... This takes me so many tries and, obviously, time to have work done properly.

Thanks