My 13" Little Squealer tends to do the same thing. I have no idea how or why that happens, but i'd like to know as well. I guess I figured it was my head (Coated Ambassador) stretching because that snare is used mainly for punk/harder stuff, so I tend to whack it a bit harder than other snares. The head is incredibly stretched right now, too (it's almost to the top of the rims) so I guess next time I could try a thicker head? Unfortunately I love the sound.
wow. I babble when I'm hungry.