A dimmer shouldn't generate QRN when it is fully off. If it doesn't have an off detent, then it is still on and may generate QRN. Some dimmers are much better at controlling RFI than others.
Touch dimmer lamps are known both as a source of QRN as well as being susceptible to RFI causing them to turn on and off and other poltergeist like behavior when you are transmitting.
- Glenn W9IQ