I just welded on an aftermarket muffler to my car about 2 weeks ago, now the muffler what used and very very black on the inside, now when the car sits for a few mins, and I hit the gas, a crap of white odd smelling smoke comes out, it never did it before the muffler, is there a way i can clean the muffler or something? and i know its not the motor its in great shape with low miles.