A lot of JL owners (including me) have heard a slight "buzzing" noise coming from the overhead soundbar when playing music with a lot of bass. It's easy to mistake for a blown speaker, but it usually seems to be coming from the middle of the sound bar.
I saw this fix suggestion form a guy on YouTube a while back and made a mental note to try it sometime. He suggested cutting some short (3-4") lengths of 3/8 fuel hose and slitting them with shears to place between the forward part of the soundbar and the upper frame edge. Wish I could remember his channel so I could give him credit because it seems to have worked for me.
He had a soft top so it was easier to access the top of the soundbar. I have a hardtop, so I had to loosen the hard top and lift it a bit. I used two Harbor Freight rubber chocks to hold the top up enough to get to the soundbar.
After cutting and slitting the fuel hose, I put four pieces to the front and inboard edge of each side of the soundbar. Loosening (not removing) the two smaller side torx bolts allowed the soundbar to move enough to insert the hose pieces between it and the frame edge.
I bolted everything back together and tested it with some really heavy bass with no buzzing/rattling at all.
I had upgraded to a set of Kicker CS speakers from Trail Seven last week, and that made a noticeable difference in the sound quality, even without replacing the knee speakers or adding a powered subwoofer.
If anybody has a better solution or, more importantly, if you see any flaws or errors with my process I'd really like to hear the feedback. But so far, this has worked for me.