Thanks for all the information, but my takeaway after reading all of this and looking at other sources online and trying some things out is that it just depends on the equipment.

In our master bathroom we have recessed lights and vanity lights. The recessed lights just had a random selection of bulbs that the contractor put in there and I never bothered to replace. Some regular light bulbs, a BR30, and one vanity bulb for some reason. These didn't buzz. Our vanity, on the other hand, consists of two fixtures with two bulbs each, and were regular 60W incandescent bulbs, and those bulbs buzzed like crazy when dimmed.

These lights are all controlled by the same two dimmer switches, and had the same behavior when being controlled by their previous, cheaper dimmer switches.

So last night I replaced all the bulbs in the bathroom with Cree LEDs. Standard A19 bulbs in the vanity and BR30's in the recessed lights. The result is that the vanity doesn't buzz (or has the faintest buzz that I don't think I'd notice if I weren't listening for it in a silent room), and the recessed lights are buzzing terribly. It's louder than any light buzz I've experienced.

I think I'll be returning the BR30's and trying another brand. It's too bad, the Cree bulbs are starting to look really sharp these days. I might try one of the ecosmart bulbs and then maybe a more expensive one and see which one is the winner.