Was that the Tetenal powder kit? The stabilizer in it is rather bad - tends to leave a lot of residue.
First check if this is in fact the stabilizer residue. Usually, it is most prominent on non-emulsion side of the negative. You can use a pec-pad to wipe it on the edge of the negative. If it wipes off easily, then it is the stabilizer. If so, I would buy a bottle of Kodak's C-41 final rinse (it's really cheap), carefully rewash the negative in distilled water and use Kodak's final rinse before drying. And from now on, just use that instead of Tetenal's stabilizer.