Weez, I have a DACT as well and they are quiet and sound excellent. This is because they have a continuous string of resistors (series attenuator) and that the circuit is never broken. When the level is changed the wiper simply selects the next resistor in the string. With a shunt or ladder attenuator there are only two resistors in the circuit at any one time. While there are some potential noise advantages (resistor noise) to this, the downside is that the circuit must be broken and reconnected each time the level is changed.
Steve refers to a make before break switch. This means that it makes contact with the next element before disconnecting from the previous one. In the case of my test attenuator it's not using this type of switch and it's a shunt attenuator, so it makes a little noise. Some folks put a high value resistor across the shunt attenuators so that the circuit is never truly broken and this reduces the switching noise. This is the case with the one I have (and older Gold Point). While quieter, it's not completely silent.
There is a lot of information on stepped attenuators on the Gold Point web site if you want more info.
http://www.goldpt.com/index.html (no, I'm not affiliated with them except as a customer)
Mike