is it for sure something about the air ride? or is that just a guess....
this might or might not help, but on my old 1989 SE, I had 2 15" subs in the trunk. after a few weeks, the subs moved so much air, that I would get a "ding ding ding" from the DIC telling me that the trunk was open, when in reality, it was the subs actually moving so much air that the DIC sometimes got a "trunk open" signal.
after a week or so of this, it got to the point where any little bump, even going down a driveway would set it off!!!
I had to adjust the latch to make it stop.
I only thought about this because you said a big speaker box was installed, so maybe this will help, maybe not