Thank you for all of your helpful posts - you know who you are!!!
After spending some way too obsessive/compulsive time trying to figure out the front seat rattle, it seems that the rattle is coming from the track when the seat is not locked into position. Like if somebody adjusts the seat and it ends up "between positions" or between notches on the adjustment rail, it shakes a bit. I found that if I simply push it forward or back a notch - no rattle.
I also spent some hot and sweaty time in the cargo area - it is in the upper 90's now - and specifically looked at the jack and stuff in that aft compartment. I checked the window wiper mechanism too. Nothing seemed to be able to make the sound I have been hearing. I am impressed by the hanging hardware and little fabric package they used for the jack. I reallt think the noise is coming from the little extension arm that secures the back door. I removed it and will see if that was what causes the rattle in the back.