Sounds like the fuel shut of solenoid. had a 2008 vintage H40 - 394 LPG truck do similar apart from the buzzing & a different error code.
Linde have modified the part a few times, it was around £80 in the UK when I replaced it about a year ago & trucks been fine ever since.
We had to use Linde Pathfinder to turn the yellow warning light out on the instrument cluster, glow plug light is used as a diagnostic light on lpg Linde.
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