Yes i had the same issue in the past.
It happened some years ago, when i stacked the seaton pairs. Back then the false ceiling didnt have any rockwool stuffed inside, and it was rattling like mad. So it was very annoying.
Then one fine day, by chance, i placed a bag of bean bag on top the subwoofers, as the cleaner was doing some vacuum work. Later i played some movie, then i realise, Eh, how come the false ceiling stopped rattling ?" i wondered. Then i saw oh, the bean bag is on the subs!! after that i got some steel shots, and placed it on the seatons pair, and it worked like magic.
Later, i built the line array. But i didnt place any steel shots above it. In one of the demos, the neighbour from eight floor came knocking on my door : “Sir, can you please lower down your bass? My windows are rattling. (sulking)”. I said sorry sorry, didnt know the bass is travelling all the way to 8th floor. (in my heart i was thinking, u need to change your windows
) But of course i didnt tell him that la. So immediately i lowered the volume.
My first solution was to get the steel shots and placed it on the line array, the rest is history, no more neighbours come knocking on the door, even with the same spls from the subs. (or maybe he eventually changed his window?) not sure. but no more knocking on the door…
that is my experience…
Happened only once with the line array…
I think the most annoying freq is 25 to 35hz… if you have a peak at MLP , its ok, you can eq it. But if this peak is at another location, then u have a lot of energy in other parts of the room. thats why i always advocate the timing alignment of the subwoofers and not amplitude response focused
if the start stop from the woofer is at the same time, there is a nicer balance of flow of energy in the room, instead of just MLP having a balanced energy…
definitely try the steel shots, it might work in your favour. at least these energy will be dissipated by the steel shots before moving upwards to your neighbour… helps for sure…