Timeline speeding up

Hi there,

I am new to resolve, I thought I would try it out as I'm looking to move away from Canon and get all BMD gear in the future. I thought I would give Resolve a nudge. So far I am liking it a lot.
I am experienced with Adobe PP, FCPX, but in means an expert.

But I am having one small issue with it.
With footage in the timeline (MP4 canon 70D footage H.264). I want to look at my editing progress, I hit the space bar and watch my edit. The problem is that as it's playing through, for no reason at all, it will start skipping frames and speeding up the music that is in the audio track...
I feel like this is an issue with maybe the fact that I am editing off an ext harddrive, and not the computer drive. I remember having a similar problem with PPCC. I fixed that by moving my scratch disc location.
Is this a similar problem? Have I done the same thing?
I'm liking resolve so far and really like the way it handles things.

H.264 material is not a good choice for post in general. Convert it to something with less CPU overhead, like DHxHD (or DHxHR), and the transcoded files should work OK.