Sometimes there are ground connections that need to be made secure in a microphone and/or its cable. It may be unlikely for two good microphones to have this problem in the same way and to the same extent at the same time, but it's definitely possible.
On another approach, if (as an experiment) you place your KMR 81 and KM 150 in an area affected by the dimmers--but instead of using the Lectrosonics transmitters, you connect the microphones via cables to a good preamp or recorder, do you also pick up the buzz then? If you find that the answer is no (and I'm not predicting what you'll find; I'm only saying, _if_ the noise goes away when you try it), then you might want to consider whether it's really necessary to use wireless transmitters in this way.
A further route that may be worth exploring is to use Neutrik's EMC-series connectors on your microphone cables.
And are you using your KM 150 with an extension cable between the active capsule and the amplifier/output stage by any chance?