I received my Gen3 sub and paired it with Arc sometime ago, and I noticed that whenever something is payed through the TV, the sub will make this constant tickling noise like a bad PC fan. I have seen another thread about this problem, and I requested an RMA for replacement. The second sub I received have the exact same problem(even a bit worse than the first one).
At this point I am not sure if I should spend more time requesting for another replacement. The noise is not noticeble from more than a meter away, but if you stick your ear close enough to the opening you can hear it. I have updated my system to the new 12.1 software, and it did not help. If this is indeed a widespread problem I think sonos should provide a solid solution for it.
What is more, the problem is inconsistant with the content I played. If I play music through airplay or the sonos s2 app, the sub makes a hissing noice which is much less pronounced than the tickling noise it makes when playing through TV. I wonder if that means that sonos arc’s capability of dilivering low-frequency content to sub is flawed?