Loose and Rattling Rear Hatch

It is possible to adjust the position of the rear hatch lock by loosening the three bolts that secure it in place, and moving the lock down as needed. The tightening torque of the three bolts is 75 in.-lb.

You will probably have to first remove the "deck trim cover rear" that covers the rear hatch lock on the bottom edge of the hatch opening, to gain access to the bolts.

 

I had similar and it drove me nuts ! Your's isn't a black Prius by any chance ?
Anyway, someone here on PCChat found a fix.
On each side of the hatch door itself you'll see a block of rubber bolted on to the bodywork - sort of U shaped.
When you shut the hatch they meet up with another block of rubber mounted in a channel that runs down the side - where the struts go when you close the hatch.
I used about an inch long piece of felt - the type with a sticky backing - on the U parts of the U shaped block. This was enough to pad out the gap that causes the hatch to rattle. At first I found I had to slam the hatch in order to shut it but after a few times it shut normaly - and no more rattles !!
Over time the felt gets compressed a bit, the rattles come back, so I replace the felt.
Hope this helps

 

There no room for adjustment of the hatch ! Better off removing the rubber bumper guides and elongate the 2 holes on the bracket about 1/8 of a inch moving the bumper closer upward toward the hatch! Apply sealant when done!

 

i found all new weatherstripping did the trick on my '08.