that's the down side of single sided cooling, try a different fan shroud or adding a second. the shroud on the umo is a very common problem, one that has been addressed by the community as a whole. for shee dependable cooling i go with gijs's v2 shroud and the right side counterpart to it, both are on thingiverse (sorry on a rush can't go find them atm, but you should be able to find them). but look around, as Ms. Frizzle would say "It's time to take chances, make mistakes, and get messy!"