Well, it has been 10 years since I built my air of BP102 loaded 20" T39s and I decided to check them out. I had never put full power to them nor did full sweeps because, back then I had to burn the midnight oil to get them completed on time, and the few times that I did use them it was for lower volume events. I did have them running near full tilt with a pair of TLAHPros, outdoors, a couple of months ago, for test and tune, and, I did notice that something seemed to be off with the subs. So, a few weeks ago I started at 40hz, gently cranked it up until I was near 30v. The first sub had air leaks at the Speakon connectors that are installed in the mouth. I pulled them out, applied a goodly amount of hot glue in and reinstalled. That took care of the air leaks. Yay!
The next sub had a nasty rattle at 40 hz with 12v applied, or 50hz with 18v. I could get it to rattle if I wrapped #5 panel behind the driver so, I figured I must have a loose brace or two. Multiple holes were drilled and eventually I found the braces. I drove 2" screws to lock in the braces, installed the driver, ran the test, and.... it's still there.

Now what!? Well, I thought of a member from a long time ago... Harley Dear. So, out came my hand saw