I have an early 04 (purchased Sept 03) and I have not had one whit of
door problems.  I cannot say that for my old 94 Dodge caravan which
rattled and creaked all the time.  I'm betting it's slightly out of
adjustment.  Hope you get it fixed because in that Sienna van it is so
quiet the slightest noise can be heard.

Are you sure the seatbelt isn't doing the rattling?

Noises are difficult to diagnose without hearing them first hand.
Fortunately, it seems as if the noise if very easy to duplicate and
demonstrate for the dealership so they should be able to fix it fairly
easily.

Thanks, guys for the help.

The dealership adjusted the latch and the contact sensor.  I guess
mine was one of a million that rolled of fthe line with this problem.
Now that the rattle is gone, this has got to be one of the quietest
cars I've been in for some time.

I had the same problem with a used Sienna.  After much hair pulling I
did find a suggestion about using a silicone spray, however it did not
quite do the job.  I then used a spray with white lithium grease in it
and have not had a problem since.  The main cause of the noise is a
plastic piece on the door jamb that interconnects with a plastic piece
(which contains metal contacts) on the door it self.  It does not take
a lot of the grease but passengers could rub against it when getting
in or out.

It worked for me, hope this information is useful.

I have the same problem with my '07 Sienna CE.  Bought it in May and
brought it to the dealer in July for this issue...they lubed the door
seals with silcone spray...I was skeptical...noise came back in early
Sept...I bought lithium spray and tried that...didn't work...brought
it back to the dealer today, told them sternly that I was not happy...
I figured since I bought 2 new Toyotas from the same salesman in less
than a year, that it might get me somewhere - NOT! (I have an '06
Tundra and love it - my wife says you can't love a truck, but what
does she know about such things)...anyways, my wife picked up the
Sienna this afternoon and said the noise was gone, but I drove it just
this evening and the noise is coming back...so now I am up half the
night searching the internet...saw a bunch of stuff about this same
issue in the 2004 Sienna...your post is the 1st one I've seen
corroborating the problem in the '07 Sienna.

This noise is truly annoying...I've owned a lot of cars and I have
NEVER experienced this...I guess I'll have to plug in some good old
rock 'n roll and turn up the volume until I figure this out.

Someone suggested wrapping black elecrical tape around the door latch
catch...that it is the latch rubbing on the catch that actually makes
the noise...they said they did this as an emergency measure for a
3,500 mile trip, and the noise disappeared....this was an '04 Sienna
and he said that the fix is actually to get a new "rough" metal door
latch receiver (the part inside the door that grabs around the catch)
and replace the old one....   I am going to try the black tape trick
tomorrow to see if I can isolate the noise...good luck and keep me
posted.

Mike