I've just had this email from WCW as a response to the video:
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Hello,
Thanks for sending this over; we've asked our technical team to have a look into this for you.
For customers who have used this backpack and previous versions, occasionally there is whining noise but this shouldn't cause damage to the unit if held for a period of 20-30 seconds but may begin to drain the battery if left for longer.
If you would like to continue to use the backpack, we have made a note on your account that you have reported a potential issue should any future problems arise.
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At least I'm covered if it goes wrong at some time.