My air conditioner/heater makes the usual rumbling noises that are pretty typical but... just about an hour ago it started to make a constant clicking noise. One click every 7 seconds, like someone is tapping the inside of it. What could this be? I have tried everything from turning it off/up to kicking the thing. Is this dangerous at all? Its going to be Sunday so I'll have to wait till Monday to call, but what do I do until then? Its driving me crazy and there seems to be nothing I can do. I have absolutely no knowledge about these things.

My air conditioner/heater makes the usual rumbling noises that are pretty typical but....just about an hour ago it started to make a constant clicking noise. One click every 7 seconds, like someone is tapping the inside of it. What could this be? I have tried everything from turning it off/up to kicking the thing. Is this dangerous at all? Its going to be sunday so I'll have to wait till monday to call, but what do I do until then? Its driving me crazy and there seems to be nothing I can do. I have absolutely no knowledge about these things.
Clicking noises are generally switches that are turning on and off. Have you tried defrosting the unit. This would entail turning it off for at least an hour to make sure that all the water that collects inside it as ice has melted and drained away. Try taking off the front of it and seeing if anything inside is moving around loose. Turn the power off (unplug it) before you do this. Good luck

If you are in heating mode, and it isn't heating, it could a dirty flame detector. Go to the sticky at the top of the forum. Read the section on sequence of operations and then on flame detectors. 7 seconds is way too long for a chattering relay.

My air conditioner/heater makes the usual rumbling noises that are pretty typical but....just about an hour ago it started to make a constant clicking noise. One click every 7 seconds, like someone is tapping the inside of it. What could this be? I have tried everything from turning it off/up to kicking the thing. Is this dangerous at all? Its going to be sunday so I'll have to wait till monday to call, but what do I do until then? Its driving me crazy and there seems to be nothing I can do. I have absolutely no knowledge about these things.
Shut the breaker off

It is so weird. The clicking has lasted about 3 or 4 hours, but has since then stopped. I turned the unit off completely and it took about two hours for the clicking to stop. Thank you all for writing answers, any info was definitely helpful. For now the constant clicking stopped but I will be calling on Monday to find out for sure what is wrong with it.

Thanks!

What kind of a system do you have? I am wondering if you have condensate slowly leaking out and dripping down on something. This would be more likely in a 90% gas furnace or if you are running the A/C. Check your condensate drain. Look around inside the system and see if there is water anywhere. Is it raining out or snow melting? Sorry to be slow to think about this.

I don't know what brand or efficiency of the furnace, but the pressure switch can cause the gas valve to open and close rapidly, check the vent and drain for obstructions.