I watched that video. Kind of funny. "4th gear doesn't make any noise." Just FYI, that's because there isn't really a 4th gear. In 4th gear, the transmission just locks the input shaft and the output shaft together. The countershaft is unloaded. The gears are always in mesh, but in 4th gear, none of them are under load. Most T-5s make a little bit of gear noise. I wouldn't worry about it. You'd be amazed at how expensive those gears are. I broke some teeth off of 3rd gear in my 3550. Those two gears alone were over $300.
Kurt