Amp/sub scratching sound

I'm pretty sure my amp may need some repair but if anyone had any other ideas I could try I thought I would attempt myself at first. Dayton 500w plate sub amp is making a scratching electrical noise via sub. Occurs with different sub hooked up to it. Current sub hooked to different amp doesnt make noise. Only occurs when amp is turned on and not in standby. I've tried different outlets, different cables, and a converter plug to remove the ground. My suspicion is either the power cable, don't have another to test right now, or something internal on the amp itself. Opening up the amp doesn't reveal anything super obvious at least to me. When noise started nothing had been altered in any way with the sub. Is power cable likely?