Bed Leveling Servo moves up and down sporadically during print

I have been using the auto bed level compensation with an RC servo attached to my RAMPS 1.4 setup for quite a while. Yesterday, I happened to be in the room for a while during a print, and noticed that the bed leveling servo was moving up and down slightly during the print. It never dipped down below the nozzle, but I have never seen it do this before. Fast forward a few hours, and a subsequent print failed on me. It had shifted 10-15mm in the X direction about half way through the print. The only thing that I can think of is that the probe dipped down low enough to contact the print. Has anyone experienced this before? Are there any firmware settings to control this? I believe that I updated this printer to Marlin 1.02, though it could be 1.01.

What is supplying the voltage for the servo? Are you jumpering the 5V and VCC pins? Or supplying another 5V source?

You are getting electrical noise in the signal cable. You need to filter the power supply with an electrolytic capacitor and shield the cable.

CDRU - I am feeding the 5V circuit through a 7805 Voltage regulator, stepped down from my 12v supply.

ggherbaz- I have a .33uf capacitor on the 12v input to the 7805, and a .10uf capacitor on the 5v output. I'm far from an electronics expert, so I was following someone else's lead. Is this sufficient? I can certainly change to a shielded cable this evening and report back.

I guess my biggest question is still why this came on all of the sudden...

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Yes, it looks like you are good to go.

This will prevent most of the electrical noise coming from the supply to the servo. But it is good idea to add a shield to the servo cable.

As to why that happened all the sudden, well let say that too many factors are involved: cheap servo constitution, cheap electronics, too many magnetic fields around or close to the servo. Been your servo so close to the hotend and heated bed, it will overheat some of its components that were not designed for those conditions.

If you're using autolevelling and your bed isn't level, then you will get movement in the Z axis whilst printing.

So I guess your bed has (suddenly, recently) become unlevel. I'd check all your connections and axes to see if there's any play.

Shielded cable seems to have done the trick... Thanks ggherbaz!