I have just installed a Fusion slim sub with a built in amp.The sub has power (green power led is on) but it is very very quiet and i can only just hear it. I have checked the power to the amp and its reading 12v on the multimeter. The RCA leads are new and are not loose. It is earthed to the floor properly ( I have scraped the paint away). I do not know what is wrong. If anyone can help it would be much appreciated.