Just when you think you've seen it all, someone comes along with something a level above!
I had a failed centre cap on one of my 4 drivers (it had become unglued, so was a simple fix), but it took me ages to locate due to the nature of it being such a hard thing to pinpoint - it had become...
I have 4 x 18" FiCar in an Infinite Baffle manifold driven by a Crown XLS 2502 2400w amp.
I built it about 18 months ago after wanting an IB for the past 15 years. It's EQd by CamillaDSP running on a Raspberry Pi 3. Before the IB, I had a single boxed 12" which punched, but didn't do anything...