Rattle Problem w/ subwoofer. no idea the model number but my speakers are 7 years old, had them

Question

no idea the model number but my speakers are 7 years old, had them stored in a box in garage for a couple months. Its a 5 speaker surround sound system. Prior to that they were hooked up to my computer. Question is what makes the rattling "paper" sound in the subwoofer and how can I fix it?I have a Fisher home stereo with ST-845 speakers. I just replaced the foam around the subwoofers and one has a bass rattle now when the volume is turned up. I used shims when I put in the new foam. Any suggestions?

Thanks.