It's not normal. I just tested my 2018 LR RWD, both driver and passenger side front doors with windows rolled all the way down (tested one a time). Neither one gave any bit of rattle. If the SC gives you the "this is normal" crap, tell them you have friends for which this doesn't happen.
It might be a hit or miss but another friend with 2018 Model 3 also does the same and the showroom car at the SC did as well. After two years I've just accepted this isn't a Mercedes