@SteCol , I am very sorry for the inconvenience, given your description, this should be the D300S fan not running properly. You need to contact support to register a return for repairing.
What is your order number please? I can inform you of the customer support email address for the corresponding region.
even my D300S makes an annoying fan noise when charging over 400watt, also despite having 3kw of panels on the roof, it does not go beyond 600/700 watts of charging even in sunny days. (sorry 'English with google translator I write from Italy)
so in the end you didn’t do the replacement as suggested by Bluetti? does your d300s get very hot? I have to keep it indoors and the fan noise is not pleasant
Fan makes noticeable noise at 400W and above. But it is not roaring. It sounds like a small high speed fan, as it was built in personal computers from 20 years ago.
SteCol can you set up your Ac 300 when using the D300S as described in the manual?? DC1 and DC2 input Source ( Other ) and PV Parallel Enable ( ON) because this configuration does not work for me, my AC 300 if the Parallel Enable is ON does not allow me to set the DC1 and DC2 du Other but automatically switches to PV