If so, you may not have a sub in there...just use the aftermarket wiring. Sounds like the guy made your life easier.
To OP, if it went from being good to rattling it probably finally blew. If you're not into upgrading stuff, just replace it. Rear seat and rear deck will need to come out, but it's not rocket science.
Welcome to the site and try and search internally or google and include acurazine and what you're looking for. This topic is frequent.