Update - Furman/Nortek responded. They said 'some of these hum/buzz'. Clearly not an answer anyone would accept, when I pushed they said simply 'return it to a dealer' and sent the general Furman/Nortek website link.
They confirmed they do NOT repair or support their equipment post-sale. They only refer you to a dealer to see if they can help. Bizarre approach to the sale of equipment that costs >$4,000. They did offer a discount on a new Ref 20i, but it is tiny and I can't see why anyone would purchase another piece of equipment from them when they acknowledge they won't support or repair it after the warranty.
They confirmed they do NOT repair or support their equipment post-sale. They only refer you to a dealer to see if they can help. Bizarre approach to the sale of equipment that costs >$4,000. They did offer a discount on a new Ref 20i, but it is tiny and I can't see why anyone would purchase another piece of equipment from them when they acknowledge they won't support or repair it after the warranty.