I was testing a batch of XTBM-Pro X10 signal analyzers, and one started to indicate errors. The configuration I use is a remote RR501 and XTBR near the panel on the opposite phase from my lab with no signal coupler to deliver very weak signals for testing. Normally that gives .06Vpp from the RR501, and about .50Vpp from the XTBR (again, on the opposite phase with no signal coupler).
The XTBM-Pro was either indicating a BSC (Bad Start Code), or the signal level was just .02Vpp when it was able to decode the command. That is REALLY down in the mud. I could faintly hear a vacuum cleaner running in the distance. Our Dyson was plugged into the same circuit as the RR501, and was loading down its signal by a factor of 3. That is a pretty serious signal sucker.
It is probably rare that a vacuum cleaner will be running simultaneous with X10 transmissions, but this might cause random errors that some folks experience.
Jeff