http://www.youtube.com/watch?v.....3PG-Gi8Xtw

This is what Daniel is suggesting:
"First trick: You no doubt notice that the open strings are a little louder/stronger than fingered notes and they also have a bit more "sting" to their sound. If you put your finger down on the string at the nut.. Where it crosses the nut and not the vibrating part.. and experiment with sliding your finger onto the string just a little ways, you can find a place where your finger damps the string just a little without changing the pitch.  - See more at: https://fiddlerman.com/forum/t.....spPostForm"
(https://fiddlerman.com/forum/s.....vibrato-2/)