VDP - Audio has loud background hiss

Hello, I have 4 Ring camera products. 2 Stick Up Cams, a Floodlight Cam and a Video Doorbell Pro. The first VDP I had died after 2 hours, but after a 40 minute call with Ring Support, they diagnosed a replacement was required, which I got within 4 days (good service!). However, I have noticed with the VDP that there is a constant audio sound being recorded, a hiss or hum. Not to the point where it prevents all sound being heard, but it is quite loud. This sound is not picked up on any of my other three cameras. I am using the Ring transformer connected to my mains electricity supply (terminals 5&6), completely replacing my existing doorbell. There is then a run of cat5 cable from the transformer to the VDP (this was previously used by my previous doorbell to activate the chime). Terminal 1 of the Ring Transformer is connected to the bypass kit. The output of the bypass kit goes to one terminal of the VDP. Terminal 4 of the transformer goes to the other terminal on the VDP. I can't attach a zip, the files are too big! The next two links are recorded from the same event (a fox in the garden). The VDP has the background noise, the Stick Up Cam does not. Stick Up Cam link: [https://ring.com/share/3d7bc751-40fb-4bc7-879f-f9384c5e15d8](https://ring.com/share/3d7bc751-40fb-4bc7-879f-f9384c5e15d8) Video Doorbell Pro link: [https://ring.com/share/bc6b671b-9e62-497e-8b3e-b4dd3e5e46c3](https://ring.com/share/bc6b671b-9e62-497e-8b3e-b4dd3e5e46c3) Is this background noise normal behaviour for the VDP? Is there anything I can do to make it go away? The sound appears if the videos are viewing on a PC, an iPad or a Samsung S10. I have deleted all app data from iPad and Android and reinstalled the apps, leaving settings at defaults.