Wow. This is incredible service, especially in this day and age. My guess is that the tech and Nissan representatives got into the 'I'm not going to let this damn car beat me' type of mental attitude.
In the early 80's I bought a five year old BMW 320i from a relative. Came with a stack of service receipts. One of the things it had been brought in for a number of times was a rattle in the console. Two of the receipts had comments from the mechanic: 'Nothing found, maybe loose change on top of console'? This was never solved. Until I bought the car, and took apart the console. The A/C evaporator was there and there were tubes which were vibrating against each other. Some nylon tie straps and some popsicle sticks and the problem was solved. It did not rattle the entire 10 years I owned the car. I solved the 'hmmm, aren't the popsicle sticks going to rot with age' problem with a very ingenious solution. When I got to that 10 year point I drove the car into the back of a Honda Accord and folded the fenders and hood up. The popsicle sticks then ceased to be an issue.