Sorry to bump an old thread, looks like there's some suggestion the bump stops can make a big difference.
Are you adjusting them via the screw? Are you raising them (anticlockwise) or lowering them?
I have suffered with a bad rattle on my 2017 B9 Sportback in the UK (RHD). I have tried so many different things, and have reduced the number of noises but the main one remains.
I have listed below everything I have tried so far. It's under an approved used warranty so if i can't resolve it myself soon i'm going to try that route, as it is loud enough for me to feel something is broken, I can hear it over music at normal volumes.
The noise. It is immediately after the rear wheels hit harsh bumps, like a line that has been cut out of the tarmac and isn't level for instance. As the suspension is quite hard it causes a shockwave through the rear and to tell the truth, the thing i think it sounds most like is the tailgate jumping up and down slightly (no visible movement though). Over long rough terrain it doesn't keep repeating it's most evident on single, harsh bumps. As the tailgate on this model is so long and quite flat, to me it makes sense that any movement would be quite significant. I think the noise is higher in the car rather than lower than the boot floor.
I think I can rule out:
-The parcel shelves because whilst they do make noise it is the same whether they are in or out
-The spare wheel/tools as i have removed them
-The rear seat bench as it's the same whether it's flat or fixed and everything in between
Rear seat bench:
-Felt between seat and plastic pillars
-Felt on metal latches
-Foam forced down the back of the larger seat portion to reduce movement
Boot floor/Tool area:
-Tools removed
-Tool tray padded out to reduce movement
-Rubber boot liner added to muffle sounds
-Temporary sound deadening under the liner
-Stuffed side pockets/fuse areas with some padding to minimise movement
Wheel well:
-Battery terminal cover padded with sponge and clamped down
-Battery cables wrapped in microfibre where they meet the bodywork
-Subwoofer checked for movement
-Spare wheel checked for movement (Removed completely for testing)
Parcel shelves:
-Felt added to 3x pins on window shelf (Now removed as it has stretched the locating pins - will have to squeeze them tighter again.
-Temporary foam added where window shelf meets seat shelf - didn't do anything
Other:
-Checked number plate surround for movement - I have removed it completely as there was movement but it's not that.
-Checked seatbelt mechanisms - Nothing obvious
-Check for felt on underside of boot latch hinge - Had the standard felt, added more, no difference
-Add felt to spring back on parcel shelf - Done
-Check if rattles reduced with centre seat down but either side up - Done, louder, not the seats.
-Check rear pillar above speakers - This was actually unclipped, have clicked it back in but it isn't the source of the noise - I had a dent removed from the roof so the lining has been out (noise existed before).
-With seats down check for tailgate movement - This i am struggling to check but want to, no way to replicate
-Add felt between rear window and plastic boot inner - Added some sponge and heard sqeaking as if there is movement - the noise was there but with added squeaking, it's possible that there is movement and the squeaking evidence,
-Add felt to rear door latches - tried it but doors wouldn't open smoothly so removed.
-Add padding between spare wheel and the boot liner - Temporary sound deadening
Todo:
-Adjust boot stops
-Check rear bump stops seated properly (Bulletin 2038689/3)
-The piece of trim that houses the boot/trunk led strip light, on one side that trim is when screwed in, it's creaking. I have tried to remove this piece but can't figure out how. Unscrewing it however seems to have resolved it so I have just left the screws out for now.