I have a amp and sub hooked up and for the last few weeks if I turn it up past 30 the sub cuts out and the protection light on the amp blinks, if I turn it down it comes back on but shuts right back off past 30? I changed the sub, didn't help, is my amp bad?
Your gains are probably set to high. When you turn it up your signal is probably starting to clip which is sending your amp into protect mode. Try turning the gains down a little and see if it still happens.
The amp must be seeing distortion of some sort. Without details it's hard to say. If you are using a line out converter from the stock system it may have a gain setting of it's own as well. The stock radio could also be distorting the output at 30. The amp you are using may not be able to handle the voltage input from the stereo when it's that loud. The amp wiring may not be sufficient for the load when you play it that loud as well.