Update on my post. Turns out all that was needed was to level the fridge. I think I had to move it at some point since 2011 and forgot to set the front back on the little pegs / legs instead of leaving the front on the rollers. I was suggested too to set up a repair appointment but having browsed around I found a very helpful Samsung page where it talks about the possible reasons for the rattling noise and that the common reason is ice buildup for which the common reason is not levelling the fridge right. The fridge MUST lean back a tiny bit.
We too have been having problem with water from defrosting collecting on the bottom of the fridge which is also the top of the freezer. Could be for that reason too.
Anyhow, I leveled the fridge by setting only the front of the fridge on the legs that unscrew from the bottom (if your fridge is full, use a 2x4 piece and place a 1" thick piece of wood under the 2x4 to create a lever, and raise it up a touch) and it's been a month since then and the noise, which had diappeared within several hours to half a day, has never come back yet.
Success so far. And it was my bad, not Samsung's.
