As soon as I turn the key into accessory mode, a rattling noise comes on:
Car is a 2007 Mazda 3 with 5 Spd manual
Does it go out once your engine has started?
Sounds blower motor/cabin filter related, to me.
Sound quietens down when I start the car (you can still hear it a bit when the car is on)
Where’s the general area of the noise? In the cabin, under the hood? From the dash? Does your car come equipped with cooled seats?
The noise comes from the dash on the drivers side ; the car has heated seats but not cooled seats
Righto, I’d check the blower motor/cabin air filter/stereo cooling fan (if equipped). Those are the simple things to check first, before needing to tear the dash apart. Are you positive it’s not from under the hood (radiator fans)?