Squeaky B String?

Just wondering if there's a nice, easy fix for a squeaky b on an S-500 Tribute? It sounds like it squeaks at either the nut or the string tree whenever i use vibrato (not the bar). I shake the string and get some squeak. Any thoughts?

Some nut lube in both the nut and the saddle. If that doesn't do it the hunt continues!-- Darwin

that is both nice and easy, thanks!