After doing extensive research on lights making sound when dimmed, it seems to be fairly normal. Often it's caused by the fact that the lightbulb, when dimmed, is essentially being rapidly turned off/on. The speed is so quick that we don't notice it though. It can usually be corrected by using high quality/trusted brands or changing the wattage of the fixture/bulb. Philips is a generally high quality brand, and Flukers is at least decent. I could experiment trying different bulbs, and may depending on the findings of the following question below.
What I can't find is if the sound can affect bearded dragon hearing after extended exposure. My thought as to why it could is mainly the fact it's a constant pitch and volume. In humans prolonged exposure to certain pitches can cause headaches, stress, etc, and prolonged exposure to a constant volume with little fluctuations (like the noise from an ac, ceiling fan, etc) can cause hearing loss.
This thread might now move in the direction of bearded dragon health instead of lighting, as the major issue is now hearing focused. I would make a post under the health forum but it might be helpful to keep all this information together.
I'm sure there are a few people here who know about bearded dragon hearing. It's not a commonly discussed topic though, so I'm not sure who to tag. I've noticed you guys have responded to some threads about hearing, so maybe you'd have some input on the matter?
@KarrieRee @Claudiusx @CooperDragon