In general, an all-in-one liquid CPU cooler will be quieter than an air cooler mounted directly on top of the processor itself. That's because the fans attached to the cooling radiator are generally larger and can therefore spin slower than an air cooler. The water pump is often well insulated, but there can be some noise from this part, however.
But there are large air coolers with big heatsinks and large fans that can compete well with the noise generation of an AIO liquid cooler. The Noctua NH-D15, for example, has two 140mm fans and is very quiet in operation. The quietest of all would be an entirely passive cooler, one with no moving parts whatsoever. However, those can't always cope with the most hot and heavy CPUs.