If your air conditioner is working properly, you'll most likely never even know it's there. Outside of a simple click whenever the unit turns on (and possibly one when it turns off), your air conditioner operates as a silent guardian of your home, providing cool temperatures whenever it's needed.
For that reason, if you do hear sounds coming from your air vents, it's worth it to hire an HVAC contractor to check it out. The problem may be tiny and can be dealt with quickly, or it could be a precursor to major issues down the road. Either way, if you know you need major AC repair, you'll be glad you have a contractor there to inspect it.
Below are a few of the sounds you don't want to hear coming through your vents. If you notice any of them, have it looked at immediately.
If you hear a high-pitched screeching sound shooting through your air vents, the most likely culprit is a fan belt that has worn down significantly and is on the verge of snapping completely. Replacing it isn't hard, but accessing it the area where the fan belt sits is the real challenge, so it's not something the average homeowner should try and attempt on their own. HVAC contractors who perform air conditioning repair often are familiar with the different makes and brands of air conditioning units, and know which type of belt to install.
The clinking metal-on-metal sound is not only annoying, but it could be destructive as well. Normally, this is caused by a fan blade that has either broken off a chip or has become dislodged somehow and is scraping along the inside of your unit, causing significant damage. Over time, this will result in not only the unit not working very efficiently, but could also cause it to stop working completely. You'll need to have this fixed by an air conditioning repair person before the whole unit needs to be replaced completely.
It's not uncommon for a metal bolt or washer to fall off the inside of your unit and clink around inside your ductwork. Though that's not a very big issue, it could be that a whole part has come off and is rattling around inside instead. Either way, it's a sign that your unit needs to be repaired, whether that's to replace a part or reattach something that's broken off.