I went out at lunch to take a better look at mine.
From behind the soundbar,
I have enough room to easily slide all my fingers inbetween the top and the soundbar.
(Not my entire hand, sorry. lol.)
In front of the sound bar,
there's a lip that comes down from the top and sits snugly against the sound bar's padding.
It sounds like you don't have any padding there.
If you don't, that's probably what is making the noise.
I still don't understand why that hard top would be flapping up and down against the bar unless it's not seated properly.
As already stated,
double check all your bolts and clamps man.