not sure if similar...but I had the exact same problem with my X3...noise coming from the trunk every time passing a bump or uneven surfaces...
after doing so many back & forth to the dealership trying to find the cause, it was the lock latch...once they replaced it, the noise was gone...
someone had to sit in the trunk while doing a test drive to find the source of the noise...
Although, I remember the sound was coming back right around the time that I was selling it...