using mostly my HD650's, i get this all the time, especially with huge amounts of that deeeep-down, thumping type of bass that you can feel as much as you can hear provided by electronica/techno/hip hop music.
to me, i have always thought that this happens because it feels as if there are hundreds of little tiny hairs in the ear canal that can easily be tickled when vibrated at higher levels from the really deep bass. naturally, this only happens with the deep bass notes and not with other higher frequency music such as certain songs using violins. nor does it happen with higher frequency music that is turned way in volume. just the certain type of bass does it for me. does anyone else experience it like i do, from only the deep bass notes? overall, i can say that i'm happy i'm not the only one being tickled crazy sometimes.
I know what you mean. On a related note, there is a sample on one of the binaural websites (I forget which won) of a women showering. There is point, when she's washing her hair and gets water in her ear, where I almost get a tactile sensation. It doesn't seem to matter too much what headphones I'm using.
I first noticed this ear tickle when I had the Senn HD 590's and I found it a bit too much at times. I occasionally get the sensation with the AT A500's but nowhere near as often. I think some headphones are more susceptible to this than others. Oh, and I always get it on the left ear.