Occasionally, a guy/gal with a Bestop Sunrider for JL, comments , on the forum, that occasionally they get a slap/bang kinda noise from the sunrider. This happens more often then not when driving at 65-7 mph in heavy crosswinds and with the sunrider in the closed position...
This noise I believe is due to lets say cabin pressure... (assuming your JL is installed properly and latches adjusted) the JL's tail gate has active venting/exhausting so air can come and go rapidly from the cab, and thus the SR fabric slaps when heavy venting/exhausting occurs..
So scenario that cause slap noises, goes like this..... wind/cross winds, suddenly, force lots of air into the JL's cabin and the Sunrider fabric is forced, stretched upward, a bit above the metal frame of the sunrider..... THEN, the active tail gate vents / exhauster, (you can see it, if you look directly behind your spare... it's named an exhauster by FCA) exhausts air rapidly, the fabric then slaps downward striking the sunrider's metal frame and causing the noise you are hearing..
Fortunately this noise/slap thing happens only occasionally .... usually when driving at higher speeds (65-675 mph+) and particularly, when there is a heavy crosswind.
So, with that said, the noise you are hearing, is undoubtedly the nature of the beast so to speak... Trade off for the occasional slap/bang, is having the sunrider in general.
I know my SR is adjusted correctly and I do get the fabric slaps, once in awhile.... Oh.... when your sunrider Sr gets saturated and dries, it tightens up a bit. The slap will subsequently be less, thanks to this increased tightness of the twill fabric....
Hint: (I do this each time I wash the sunrider)
Assuming you have the Twill fabric.....When you wash/soak your sunrider, or when it gets soaked from the rain.... when the JL is parked, release both latches and lift the sunrider up a couple of inches.... Now, let the sunrider, fully dry... this will allow the sunrider twill fabric, to tighten up as the latches are not restricting the sunrider from lets say ..... for a lack of a better word.... shrinking.
The above is also something you can do with any convertible that is made of cloth type fabric...