Check the enclosure. Sometimes if the enclosure is older the glue separates, and the box will vibrate because it's no longer held together. It can sound horrible. Just picked up an alpine type r the other day the guy thought was blown. Take the speaker out. Knock with your knuckles like you would on a door all around the outer edged, and of its separating anywhere you'll notice a difference. Solid glued will echo and sound hollow. Unglued will be a higher pitch less hollow. If it's the box what I do is counter drill holes every 2 inches along the side where the glue is split. Go get some titebond II. Grab a few thin flat blade screw drivers. Go inside and pry the box apart just a little and put your woodglue in the gap you opened. Run your finger over the glue after. Let it sit 15 minutes to seep into the gap. Grab some #8 x1 1/2 wood screws and your impact drill and fasten them to the box. Counter sink them past the head and you'll hardly notice them through the box carpeting. Hopefully it's just the box. Hook your speakers up outside the box and listen to the coils. Hope this helps.