Annoying hum from 5D3 enclosure

I have an annoying hum coming from my Drobo 5D3, which I can reduce by 1) removing the drive bay cover, 2) placing my hand against either side of the enclosure, and 3) shutting down. I’ve tried placing the Drobo on an old mousepad, but that hasn’t helped.

I’m open to suggestions. Thanks!

You seem to be describing a harmonic vibration in the Drobo external shell, created by the HDDs rotation.
You can try to offset this by positioning your Drobo on its side - it won’t affect its operation. To do this purchase 4 adhesive 5-7mm deep silicone feet/bumpers and adhere them one side panel of the Drobo. The more plyable and deeper the bumpers the better the dampening.

I’ll give that a try.
Thank you.

So far, this appears to have worked.