Larsen effect/feedback/tone on the Line IN input on Hiwatch DS-H216QA(B)

GiovanniG

Young grasshopper
May 18, 2021
60
7
Italy
Hi mates, when I enable the audio I have this annoying tone as result, no matter what I connect on line in, connected, disconnected or grounded. How can I get rid of it? The FW is updated V4.70.143 build 230418
It looks like the two way cannel is always enabled and there is an hardware impedence between audio in/out, that generate the problem, maybe dust?
Thank you