I returned to the site today to see if I could look further into the temperature differences. I pulled the failing n3 out of the rack and placed it on a table. Before I pulled it and while it sat on the table, it would run at about 53 degrees while the other n3, which has never exhibited this problem, runs at about 38 degrees. I removed the top cover to check out the fans, the three of which I could see appeared to be working properly. As soon as I removed the cover, the temperature as reported via the front panel began to drop. I reinstalled the unit in the rack without its top cover and let it warm up for a few minutes. Its temperature leveled off at about 42 degrees. Given that it has four input cards as compared to the other unit with three output cards, that may account for the slightly elevated temperature. I've left it like that and we'll see what happens....