Try re-booting from a cold start. Shut down both computer and interface.... wait 10 seconds and restart both.

I get a strange zipper-like sound at times and a reboot always solves it.

The ASIO drivers should be the ones to use with the focusrite. I have a focusrite as well. (Sapphire) every now and then something happens to the stability of the computer and the reboot is always the fix.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.