So chime is buzzing as motion is activated at video doorbell, voltage at chime and button contacts is 13.35v chime is rated for 16v and video button is auto ranging 10-35v, so within voltage range, just lower at the chime, video is skybell HD and chime is Nutone , transformer is lost somewhere in buried closet ceiling or attic, house has had extensive remodel and owner and wasn’t happy with EC ? From builder. The lower voltage on chime wouldn’t cause chime to buzz?

Huh??

I have absolutely no idea what you are trying to say.

If you are saying you have 13v at the chime and it isn't chiming when the spec is 16, you might have a bad chime ... (unless they are talking about DC in the chime spec)

Trying to find out if it’s normal for camera to activate the chime coil, and/or if the 3volts drop from transformer would cause any other problems, I know we have to find where trans. But the chime buzzing is a annoyance to Home owner, I checked if possible reverse polarity at chime but has no effect?

As Greg said, do you have a bad chime??

The 'buzz' is the coil(s) trying to activate the plunger to 'chime'. Is the chime 'new'? Was it in the home during the renovation? Could be spackle dust, or worse.

Simple step #1 is to try another (known good) chime.

Chime works with single note, assuming it would double strike if receiving full 16volts, just trying to confirm with someone who has done more video button installations, thanks

Most chimes that I have seen strike twice for the front door and once for the back door.
Could you be landing on the wrong terminal?

Sounds like Ghost is on the right trail.

I didn't include that comment, OP did not say it did a single chime, just that it buzzed.

No it’s on the right terminals, just that the voltage has dropped, is why I believe it only has power to strike once.

The skybell video door button, has a motion activated camera and sound, runs through WiFi to cell phones etc, but get power from bell transformer, and seems to be activating the camera, puts humm on chime transformer, just trying to answer if that’s the normal operation of these new video door buttons, manufacturer just says it could be since the chime isn’t receiving full 16 volts? not whether that is normal side effect of video button unit?

You could disconnect the wires at the smart button and see what you have then (assuming this is just a doorbell circuit)
Usually the power goes into the chime and they run a switch loop to the button. You should be able to ring the chime straight from the transformer leads. If that doesn't work you have a bad transformer or a bad chime.
I suppose you really should find the transformer and remove it if it is bad or at least remove power from it if it is hanging outside a box, buried in the wall and find an accessible place for a new one.

Is there any chance that the chime wiring has been run in parallel with higher voltage cables, causing an induced voltage at times?

So got into attic seems to be older type install with individual conductors run to each device, typical of older system installed with knob and tube era, where trans former is spliced off K&T wires and nailed to side of joist,

What are the chances you can just run fresh wire or use the existing with a regular transformer.

So rewired the chime and located new transformer in accessible attic, got 16 volt trans, read 20.4 at button contacts, chime still only strikes once, on front contact. could the chime be blown since only receiving 13 volts over time?

Is there a terminal for one chime and another for both?

Did you test the chime with the new transformer directly connected?

I'm just noticing this thread. Sounds like the door bell is just the old style with a couple solenoids. you press the front door bell button and the solenoid's armature strikes the first chime(Ding). Release the button, and the spring sends it back to hit the other chime(Dong). The back door bell button causes the 2nd solenoid's armature to hit he 1st chime(Ding), but the spring return doesn't cause it to hit anything.
A typical button is open or closed, or perhaps there is an very hi resistance light in the button. No big deal. But if your button becomes a parasitic load, it's flowing current all the time. Maybe enough to cause buzzing. So you push the button, you cause max current to flow and you strike the first bar(Ding). Then, you release the button and the parasitic load still allows enough current flow to fight against the spring return. (No Dong) So in a case like that, you would need to use an interface between the old and the new.
Joe

I didn't see any statement about this problem being resolved. This is what I would do to fix it. I would insert my Fluke in the line between the front door chime screw and the front door button/new parasitic load. Test leads in "COM" and "A", Switch to AC A/mA. After any initial, power up, current, settles down, I would record the standby current. Then I would switch to min/max record and ask someone to enter the motion sensing range, I would record the max as the current that should ring the chime, and the steady state current after that, as the parasitic load while it's sending, recording, et,c. Finally, I would have them push the button, and record what I would expect to be the maximum current that should ring the chime. That's it for recording data.

So initial motion sensed or button pressed current should fire the solenoid, but no current less than that. I could perhaps use a current relay between TX HI and the button. Its N.O. contacts would go between the front door screw and TX LO. Only the 2 higher currents would pick the relay and ring the chime.

I would probably prefer to use a source resistance like they mention in their manual and insert a small bridge rectifier in line. I would have the bridge feed a little opto triac circuit, that would fire the chime. Either of these two methods could be used in an interface that they would sell you. But, all in all, I'm not too impressed with what I saw from these folks! How hard would it have been for them to lift their load long enough to allow an armature to return?
Joe

Located new transformer 16v 30w and refed the chime and spliced onto wires in attic that led to button, seems to work as as needed, still there's a unknown splice location in old wall house to mudroom.

I just noticed this thread as well, the early models of the Ring door bell required a larger transformer if you wanted to activate the local chime at the same time as the networked chime, a 30VA. Skybell may be the same. The newer versions do not require a larger transformer as they are battery powered and the existing transformer just keeps them charged.