I would have them to install the 2 Shot Relay and replace the Trunk Pad Release and inspect the wire harness at the trunk pad release.This just started happening to my 2011 LaCrosse with 22k miles on it.
My husband brought it to the car wash and ever since, the trunk randomly opens when it's in the garage with the doors unlocked. Note that we do not carry our key fobs. They remain in the cup holder in the garage, so we can't be pressing it accidentally. We also took both of them and put them out of range and the trunk still opened.
I had the car at the dealer for something else and told him about the trunk opening and after looking at it, said there was nothing wrong. I brought the car home and the next time I went into the garage, the trunk was open. It has not happened when the doors are locked.
I had originally thought we were closing the trunk too hard, causing it to pop back up, but we have been closing it gently and it still does it.
From reading here, the 2 shot relay may or may not work. Considering this started after we had it washed, I'm wondering if something didn't short out.
I'm about to call the dealer back. If this continues, I'm going to sell the car. I don't need this headache. This may also be our last Buick. It's the second defect that's popped up - the first was the GPS fin stopped working for no reason when the car had 2k miles on it. This car is really only used on the weekends. It shouldn't have these problems.
The trunk should not open on its own if the doors are locked but it can. I have not heard back from Buick if there is a permanent fix yet.