I noticed that a lot of people experience this same issue and don't know how to fix it. Here's one simple setting that completely fixed it for me. This video is a little different from my recent uploads, but this is just too important not to share.
This works pretty much the same for all DSLRs and external microphones. Most cameras have a sound recording option, so make sure to go and change it from auto to manual when you use an external microphone.
Music:
Dj Quads - It just makes me happy