Boss BV7334 3.2-Inch DVD/MP3 Receiver with 2 6x9-Inch 400W Speak "car making hissing noise" Questions

...hissing noise from the speakers and the amp is a 4 channel amp but all 4 channels are positive all 4 chanes only have 1 rca in put what else could i do? or doe i need to separte the rcas with the Y's ...