I never had this problem before in the 10 years we've lived here, but in both toilets, in a pattern like it sprayed out when the toilets were beginning to flush, there were fine, black particles left on the inner side of the rim of the bowl, above the jets. People tell me, that, because of Irene's rain and then Lee's left over rain in the northeast, there has been more mold around. Could it be coming through the toilet jets?