I have my new liner installed and have been burning for a about 2 month period. i noticed last night that the top of my chimney cap is really black and looks like it's dripping off the top it. well it's not dripping it actually looks like it was water it is frozen. but it's black in color. should i need to worry about that, it still drafting good and burning good. i just thought i would check it. my father inlaw has the same problem but he hasn't done anything about.