if you smell it when driving HARD for a while,
than it is some "heat protection" near the exhaust,
also the expansionjoint between collector and exhaust might be melting, that will be vanished when you hear you have 3 exhaust-noizes, 2 at the back and one in the front
conclusion: you drive too hard!!!!

but don't have to worry about it
(I have joints at home because I "burn" them rather quickly)