I went to fly today, and the 2 rear motors would not operate properly. No matter what the throttle or control inputs were, the motors would only spin about a constant 50 RPM in a very choppy motion. No crashes or any other issues ever. I reinstalled all drivers and firmware, recalibrated, to no avail. I am going to think about opening to check for a cold solder some where, as has been reported, but I am afraid of voiding the warrantee. Has anyone experienced this or have any ideas? Thanks...