Heater Smell

When I use my (cabin air) heater, it starts to smoke a bit and smell if
I turn it more than half way up. I suspect that this is coming from a
build up of material in the heat conduits over the years. Does anyone
else experience this? Should I have my heating hoses removed and
cleaned (seems expensive if I have my mechanic do it)? Could there be
something more significant going on (by the way, I have a CO detector, I
have not significant CO, so I know that I do not have exhaust fumes
leaking into the cabin air heating system)? Suggestions?


-Sami
N2057M, Piper Turbo Arrow III