i have a similar noise issue with 2 x red pro 10 TB hard drives… not the buzzing sound at the beginning of your video but more like the clicking that follows it.
did you return and replace the entire PR4100 3 times? same noises with each replacement? i submitted a case to WD Support for my situation, not very helpful- they pointed me to the same “How to tell if the noise…” link, then i responded to let them know that the Data Lifeguard Quick and Extended tests passed successfully, and their response was to RMA the drives- how are they coming to that recommendation?? i provided no feedback to indicate that the noise issues i’m encountering are problematic- i made note of this to WD Support and have received no response since, so i’m less inclined to RMA the drives now.
at this point, my gut tells me that the drives are fine, as there seems to be a pattern of users reporting similar issues, which i think means that my issue is not as likely to be a one-off bad set of drives. i don’t want to RMA the drives only to receive two new ones that have the same noise- i feel like maybe this is what happened to you? my biggest concern with keeping the drives is not knowing for sure if these noises are considered normal, and then one day they quit- wish i could get a straight answer from WD Support…