I noticed things like this before when looking back over collected data:
I was just looking at the live data stream and saw one currently active. It suddenly dawned on me that what I was looking at was out washing machine on its spin-dry cycle. Watching it to the end confirmed it, as the spin cycle ended and the drum slowed, so the trace I was watching dropped off.
I am more than a little surprised that my S-Boom picked this up. Based upon this Google Earth measurement, the washer and S-Boom are ~32m apart.