2009 Fox 36 Talas RC2 Buzz Noise

So I've been having some problems with a buzzing noise that I thought was my rear tire buzzing the front Deraileur or my front brake line buzzing the front tire (I could never isolate the problem) but today I think I know what it is. I was climbing and put the fork in 140mm travel mode and everything was cool... when I got to a more flatter section of the trail, I put the fork back up to 160 and rode it for a little bit and then hit a section where I g'ed out and there was the noise.

Specifically something I did which brought the noise on even more, was to turn up the low speed compression an additional click (from 4 to 5) -- it was more noticeable when I was in the 160 mode.

so anyone have a similar problem? What is it? What's the fix?