E92 Parcel Shelf Rattle from Bass (Sub in boot)

[sylonien]

So.... finally managed to install my subwoofer in my E92 M3 with HiFi audio.
But unfortunately immediately there is massive vibration / rattle from the rear parcel shelf.

I can see it bouncing up and down from the mega bass.
I looked underneath and there seem to be a small gap hole between the parcel shelf and the boot area.
I guess that's blasting the sound through that bit
and causing it to rattle like mad.

Not sure how to fix it. I tried stuffing that hole with foam but its rattling.
Next step is to try and remove the shelf and dynamat it like mad?