I don't have any guess about the noise in the trunk, but I agree that shocks are likely from static.
I have cloth seats, and since putting sheepskins on the seats a couple weeks ago, the shocks are extreme!
Next time you are ready to get out of the car, try this -- with the door open, look over to the left, and down at the left side at the back part of the car where the door latches when it's closed. There's a U-shaped unpainted hook there for the door to latch into when the door is closed.
BEFORE you slide across the seat, hook one finger, or your thumb, into the U, and leave it there until you're out of the car. If you don't get shocked that time, it's been static.
Keeping your finger on the hook lets the static run down into the car body as you move across the seat, and not build up in your body, so there's no shock.
I have to do that everytime I get out of the car, or I get zapped. It's a small price to pay since I love the sheepskins.
If what I'm describing doesn't make sense, let me know and I'll post a picture of the latch hook.
The back-up issue is a big thing, and worse for me since my last car was much shorter. I put blind spot mirrors on both of the side view mirrors, and that's helped me a lot.