If working properly, the only sound you'll ever hear from your AC unit is the gentle hum of it turning on and off. If you start hearing it creating more sounds, such as a clanking or a high-pitched whining sound, you'll need to have it checked out by an HVAC company, which might recommend AC repair as well. Below are some of the sounds that you do not want to hear coming from your air vents. Beyond the fact that they're simply annoying, they can also represent significant problems developing in your HVAC system.
A clanking sound that is rattling through your house is usually caused by a bolt or a part that has come loose and is banging around inside your vents. This can be either a minor fix, such as simply reattaching the bolt, or it could require a larger AC repair job, consisting of reattaching fan blades. Either way, this is not something you want to tackle yourself, since getting inside the unit repairing the issue is complex by itself.
An old fan belt that is straining to hold together under pressure can create a high-pitched whining sound that only pierces the eardrums but can also snap at any moment. Once it does, your AC unit will still operate, but the fan blades won't push any air out to your home, which will make temperatures rise. Regular AC maintenance will be able to detect when these belts are about to snap, so make sure your technician looks at it during the regular service trips.
One of the worst sounds you can hear coming from your AC unit is a screeching, metal-on-metal sound. There's usually only one cause for this: a fan blade has either dislodged or has chipped off a piece that is scraping against the inside of the AC unit. If left unattended, this can cause significant damage to your home's AC unit and even cause it to be replaced completely. Schedule an AC repair service to have it looked at and repaired.
As mentioned above, a simple clicking sound is normal for when the unit turns on and off, but if you hear the unit clicking repeatedly during the cycle, that means that the system is having electrical issues and is probably trying to fire and re-fire to make the unit run. Eventually, the system will go out completely and you'll need to pay for a full replacement.