Our equipment has very low hum and noise. 99 out of 100 times hum comes from ground loops in the system. Ground loops pick up the hum and noise in the air and this gets amplified. Good grounding is very important. Ground loops can occur if all equipment is earthed, the ground is connected to the earth pin in the wall sockets and all equipment is connected together by the interlinks. Mostly the hum goes away when for example some of the equipment are put in non earthed wall sockets. You have to experiment with this for best result. It is very hard to predict what is the best layout.
Sometimes hum also comes from too high sensitive systems. If high output amplifiers are used on high sensitivity speakers and a pre amplifier is used with a lot of amplification, systems can get very sensitive. Typically the volumecontolr cannot be turned higher than the 9 o'clock position. This means you have to damp about -40 to -60dB and than amplify up again. Pre amplifier output than is in the order of mV's (Like MC cartridges on turntables), which easily picks up hum or noise. Best is to get less amplification, but if this is not possible using for example a -20dB Passive active damper at the input of the power amplifier also will solve the problem. It reduces the input, meaning the pre amplifier has do do more works and signal to noise ration will increase with +20dB. | 
