Merge Clips Smashing and not keeping clips in original format

When I try to merge clips together sometimes they stay in their original form. Which is what I want. But other times, it smashes the sound and it's no longer in it's original form. It seems completely random. I can't figure out what I do when it works and when it doesn't work. I can't spend hours editing the audio just to have it ruined when I try to merge clips, so I try and try and try until it works. But it's extremely frustrating and time consuming, and still seems random.