...it causes audio feedback and echoing...
You are hearing audio feedback, which means you are hearing it from some output. So which output is that? Is the feedback heard on the VTO/doorbell's speaker,
a VTH speaker,
Blue Iris (computer speaker), NVR speaker, phone app?
Is this VTO connected via (UTP and POE) OR (WiFi and DC power supply)? If WiFi, you might consider that what you are hearing is not feedback (in the
traditional sense - meaning there is a direct audio link between and output and input which gets amplified in a loop), but rather an issue with the
digital audio being corrupted/out of sync/distorted from the nature of WiFi.
If it is connected via (UTP and POE) you might check the termination of the RJ45 connector at the VTO. I like my VTO's, but because the doorbell is
typically mounted plumb, the UTP has to make a 90 degree bend over an inch and a half if you connect it intuitively. It depends on the construction
of where you are trying to mount the VTO, but I tried to run the UTP at a 45 degree angle from the bottom to ease the strain/bend on the connector:
