That's a long time to live with an unusual smell. Hard to say; some people are bothered by the wiring under the dash, the carpet, the headliner, the upholstery and the rubber gaskets around the windows. Or perhaps mold in the ductwork.
Some smells are more characteristic, like a sweet aroma you sometimes get with a heater core leak.
Ask your dealer to try some BG Frigi-Fresh in the ducts if that hasn't been tried.
Meanwhile, if you toss some fresh ground coffee on the carpet, that will help mask the smell for a couple of weeks.