I'm inclined to side with the paranoia lobby, however if memory serves, can't channelers sense Gray Men?  The scene I'm thinking of is the one from tDR after the Stone of Tear had been taken.  Rand is in his chambers, I believe with either Berelain or Lanfear, and he senses something weird, eventually spotting the Gray Man.  I believe this is right before the Trolloc attack, so It must've been Lanfear in the rooms with him...either way, I'm fairly certain he sensed...something.

 

But that's just my opinion.  I could be wrong.   ;D

a couple times the Grey Men show up Rand senses something and smells something like death around. correct me if I am wrong