Hi, I have a Day&Night central forced air unit that will make the large duct work that connects to all the smaller ducts to it vibrate and it makes a vibrating noise so loud that we can hear it upstairs. When I first turn the unit on it will be fine but after a minute or so the vibrating begins and after a few minutes, it trips the breaker. Also, I get no cool air from the vents at all. Thanks for any advise.

I believe you have a blower motor problem. Take the blower panel off and start it up to see if the blower motor works or is vibrating. Also just for fun check your air filter.

I agree, sounds like a motor problem, maybe the bearings.

Could just be a mouse or something stuck in the blower wheel, sounds funny but we see it all the time.