1998 Pontiac Grand Prix Rear Speakers

I bought this car a few months ago. It's previous owner really didn't maintain it as it should have been. Anyway, The sound system, specifically the rear speakers would work most of the time (occasional infrequent popping noises) but now doesn't work at all. I heard that those speakers have subs included in them. I paid $100 for this car as the previous owner thought a bad water pump was a costly-to-repair head gasket leak and was ready to sell to junk yard as scrap. This car is straight as an arrow and now runs like a top (I have invested about $800 into it). I am now wanting to replace the speakers, but it is my daily driver, and tearing into it and finding a suprise is what I would like to avoid. Thanks in advance for your help!