Ive got two questions,
First of all, I have a 2008 Mazda3 and was wondering if the stereo is ready to put a sub or two in it? If not what do I have to do to get it ready?

Number two, there is a knocking noise coming from the engine compartment when I'm at a standstill, but if i get out and check the engine or anywhere else in the car, I hear nothing, only when inside.

Please help.

 

well regarding stereo part is if you have original mazda 3 stereo than u need a kit that will connect to your wires in stereo connection in order to have an output for amp (audio output) that will run to your subs simple to do it i have done that once till i got a 7inch touch screen ... so basically connect amp first and subs are easy to connect to amp 2 wires lols or matters upon how many subs and type of subs lol

 

Where do I getone of those harnesses?