The first thought I had reading about your application did make me wonder if there would be a bad mix between the Pi PoE+ HAT and the coil-whine experienced on some boards. I can see you already found the thread discussing some issues identified with those boards.
In summary, we have found some boards are very noisy while others in the same batch perform as expected. If you have received a board that is noisy then we can get either a replacement or a refund sorted out under RMA.
