[shorod]

Depends on the noise. I'm not sure what you mean by a "weak noise." Are you saying that the amplitude of the bass decreases as you increase the bass setting? Does the bass sound distorted? Have you had the sub out of the box and the wires disconnected? If so, you may have accidently reversed the wires and now the sub is playing out-of-phase with the rest of the speakers, essentially cancelling the bass frequencies out.

If you listen to the factory stereo at high volumes with the bass turned up quite often, there is a good chance that the sub has been distorting for quite some time and that has damaged the sub. The voice coil is weak and limited on the amount of excursion, so as you turn the bass or volume up, the sub is limited by the amplitude that it can provide, giving the impression of getting quieter.

-Rod