Motors spool up on ground with no pilot input

Hi, we had something odd happen with our quadplane, i can’t see what could have caused it in the logs but hopefully someone might be able to shed some light on it.
Just after the 31 minute mark in the logs while sitting on the ground - armed but with throttle at idle 2 of the motors spooled up to around 1600, one to 1300 and the other stayed at idle. Any ideas what could have caused this? Log is linked to google drive https://drive.google.com/file/d/1h6_po99zIoSJXtjH-Y9TfoSWFek4yHSX/view?usp=sharing