We normally use three packs as well. If on a freighter, then only 1 pack is frequently used to save fuel I suppose.
As stated above, the packs are very noisy outside due to a high pitch whine from the compressors which are annoying even if standing well in front of the aircraft. Even though you are far from the APU(which is in the tail), earplugs are definitely required when doing the walkaround underneath the central part of the aircraft as it is extremely noisy due to the exhaust air and the high pitch whine from the packs. As well, on warm days there seems to usually be a lot of water coming out of the panels on the belly in the area of the louvered pack exhaust outlets(and some jets of high speed steam out of some small circular vents).
On a hot day, depending on the wind direction and strength it can be really uncomfortable checking the wheelwell area due to the very hot exhaust air but it makes up for that with a nice warm breeze in cold locations.