Brand new Mazda 3 sounds like a damn Toyota Echo?

[RotaryLover]

Maybe it's the break-in period, maybe it's me and I have paranoia for nothing, but when I drive my 2010 Mazda 3 with the windows open and I press the accelerator it sounds like a old Echo or a car that has the Catalytic Converter removed...like a buzzing sound. If I press the accelerator on Neutral you dont hear it. It's all silent when I dont press the gas or at Idle

I've also noticed that I did about 330 km on the first tank of gas and I've wondered if it was related to the Catalytic Converter. If it helps it's the 2.0L 4cyl.

Any ideas on what's going on? Thanks.