definately make sure the ohms are matching up. and make sure your rms on the amp matches or is relatively close to the rms on the sub. its possible that your sub is trying to draw too much power from the amp if it cant put out enough, thus making it go into protect mode. Alos, be sure that all wires are connected securely as a loose power wire can do the same thing lol. What model subwoofer and amp do you have exactly?