we haven't shipped out TC420's for almost 6 months actually, we have the improved wifi enabled model aka TC421. We do bench test the entire system as ordered before we ship out so yes no dimmer tested in this case but there should not be buzzing in any case unless there is a fault with the dimmer/controller.
Noise on dimming with the TC420 happens very rarely and past experience shows that this usually only happens if power is applied via the DC jack instead of V+/V-. The DC jack is only meant for very low loads e.g. power to program the TC420.
It has however come to light very recently (yesterday) that some (not all) of our 100W waterproof power supplies (only the 100W model) do buzz under certain conditions and we are investigating the cause, only the 100W, all others are fine. As a precaution we no longer ship the 100W out with any system even if it tests 100% ok and substitute it with a different model, 100W are now marked out of stock until we get to the bottom of it. Colm yours slipped out the door before all of this so lets assume the power supply is the culprit and replace it, we will cover the cost of doing this. The closest suitable one we have for your tube is 80W, let me know if ok.
Cheers, Fred