I have a Rumble 15 that had a blown speaker, and for jollies, I thought that I would beef it up a little. I lined the cab with damping material and put a speaker that I had lying around in...I now it may not be optimal for this cab, but what do I have to lose by experimenting? The speaker: http://www.parts-express.com/grs-8pr-8-8-poly-cone-rubber-surround-woofer--292-428 Now I get some farting out noises, even at a lower volume level where there weren't any before. Could it be lose joints that need glue? Need a speaker break-in period? Any advice would be great! Thanks!