Ratchett

I just replaced my stock AST with the aluminum pettit version. When removing the old one I noticed with a little alarm that all sorts of crap came out of it, bits of black stuff (like spots of rubber) and whiter chunks of solids that looks like calcium deposits to me. Does the position of the AST in the system ensure that impurities gather there, so perhaps this is normal .... or not? Car runs fine otherwise.