When I had to RMA via Noctua, I contacted them via their form and had a reply in very short order (a day or two I believe). Entire process of RMA entry and new fan was very quick and fast. However, this was before the pandemic hit, so it might have been a bit slowed down compared to that. But should still be fairly fast in response, assuming you submitted your RMA to the right location.
Also, may I quickly ask, what are you using your U12A on? And how is it connected to the motherboard? Which motherboard is it? As the Noctua (and many other PWM) fans are known to make ticking noises when a motherboard fan header it is connected to is actually giving off voltage control instead of proper PWM signal to control the fan speed.