<font face="Arial, Verdana">I've had this happen before. It looks like switching power supplies worked for OP, but if anyone else has this issue, try this:</font>
<font face="Arial, Verdana">#define Z_PROBE_START_SCRIPT "M340 P0 S2290\nG4 P2000\nM340 P0 S0"</font>
<font face="Arial, Verdana">#define Z_PROBE_FINISHED_SCRIPT "M340 P0 S800\nG4 P2000\nM340 P0 S0"</font>
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<font face="Arial, Verdana">This waits 2 seconds (long enough for servo to move) and then stops sending signal.</font>
<font face="Arial, Verdana">The only time this didn't work was on a ultimaker 1.5.7. Somehow on that board my servo was affected by hot end PWM, so the hot end had to be off for the servo to stop twitching, </font>