Two weeks ago I bought a 2004 Crossfire demo with 1000 kms on it. I love the car. I have noticed though that the car is sounding noisier above 3000 RPMs than when I first bought it. When I first started driving the car, the car sounded very smooth accelerating above 3000 RPMs but now when I accelerate above 3000 RPMs it is noisier, slightly tinny sounding. Could this be a result of a change in fuel? I drove the car off the lot with a full tank of gas, but I don't know what kind of gas the dealer put in the car; they may have filled it up with regular unleaded gas. I've been putting premium gas in it since then. Maybe the sound the car makes now is normal with the higher octane gas. Any ideas? The car itself still performs great -- no change there -- and the oil level/condition is fine... no instruments indicating any issues either.