I have a JL 500/1 amp going to 2 memphis 10s. When we first installed every thing sounded great and plently of power. After a few days the amp went down on power and under cold start up it makes a buzzing or hissing noise from the amp. When the subs hit it goes away for a second , but it comes right back. at first it was making the noise for a few minites ,but know it is like 5 minintes after the start up. Does any body know what the noise is or why it doesn't have the power it used to??