Mk subwoofer, may need repair (Maple Leaf / Northgate)

Miller & kreisel v-75 mark is powered subwoofer. We getting some feedback when we unplugged it and put it in storage 2 years ago. Didn't bother troubleshooting so no idea if it's a serious problems or just interference. Too big for our space. Coordinated pickup so it doesn't get rained on.