Pk - Subaru's doors have been famous for being incredibly tinny sounding when shutting. However, Subaru's door framing (a & b pillar for example) is obscenely strong. So the car is solid, but it doesn't shut with solidity mainly due to the frameless windows.
If your passenger side was t-boned, my guess is that the body shop put it back together nice and tight. Might want to look at taking the driver's side door off altogether and re-starting from scratch, if it bothers you that much. Did you notice it progressively get worse, or just one day "there it was"?
You might also be able to put in some un-obtrusive rubber bumpers that dampen the door shutting and hold it very tight.
Just some ideas....such a minor thing that happens before you even drive off to let it bother you
