30 mph standing still

I'm thinking spedo sensor is dirty or getting wonky ?
I fired up my 1995 k75 for nice long ride today .
Bike fired right up and ran perfectly as it always does ...
But approx 1 minute after starting the bike , while it sat idling ,
over the course of 10 secs I saw the spedo move from 0 to 10 mph , then briefly up to 30 mph , then dropped then drop back to 0 . The bike and spedo then ran flawlessly for the next 300+ miles
Tempted to run it until hard failure , so long as it does leave me on the side of the roadside somewhere ...
Any ideas ?

Regards ,
Todd

I clean my speedo sensor at least once a year when I get those wonky speeds. It seems to clear things up for another year or so.

It has been a while since I had a K of this vintage, but my recollection is that the speedo is electronic and for it to be moving requires an electrical input. If my memory serves, a test to see if the sensor is working back in the day, was to put a working soldering iron tip near the sensor after removing it from the FD. The alternating current RF (I believe) gets picked up and interpreted as speed impulses from the wheel. If your speedometer is jumping with no movement, I am guessing there is something interfering and inducing a current into your sensor line. Short in the wiring? Something else malfunctioning?
Others with more experience will know better, but if it is jumping while not moving, I would not think cleaning will help. That will help with wacky readings while moving, BTDT....