Trunk

I cannot answer you LaCrosse question for sure but on earlier Buick Riviera/Reatta, some owners have had problem with the unlatch solenoid involuntarily cycling. Just recently I looked at one where the trunk and door locks were doing that and we are pretty sure it is the keyless remote module that is causing the problem. On the car I saw, we unplugged the module and the problem went away. The owner was going to get another module but I have not heard back from him. I do not know where the module on your car is located but on the Riviera it is on the underside (trunk side) of the rear package shelf. (under the rear window)

Thank you