Most Ramps boards require some form of cooling, in my case the "Stock" Ultimaker cooling fan was making a lot of noise so I redesigned the cooling shroud, to retro fit with easily available 50mm PC Fan's with Ball Bearings (mine were 12 Volt StarTechs TX3/LP4 50mmX10mm).

STL files can be found here :- http://www.thingiverse.com/thing:1147173
Be sure to place one fan upside down, so that one fan sucks warm air away from the Ramps stepper drivers (i.e. the one with the 5 tiny heat sink boards) side opening and the other fan blows cold air into the second opening, this will give a much better air flow.
Wire both 12 Volt fans in Series and connect to the 24 Volt supply that was originally driving the old (noisy fan).

Please Note !!!,you will need to attach feet like http://www.thingiverse.com/thing:1147140 as this shroud needs more clearance beneath the Ultimaker, these will accommodate the new set-up.

I am using 4x10mm Bright slow colour change LED's... as the forward voltage is 3.3V I connected 4 in series and supplied them with 12 Volts.