You need to pay attention to the sounds that come from under the hood of your car. You should know how your vehicle sounds, and you should know when you need to be worried about the sounds your vehicle is making.
If your car sounds like metal is scraping against metal, the most likely culprit is your brakes. When your brake pads are thin, there is metal under the pads; when the metal on the brake pads encounters the clamp on your brakes, it can make a really awful noise. You will hear this noise when you are pressing down on your brakes. You shouldn't hear this noise when you are just driving around.
A clunking sound can sound like your car is hitting up against something, like two pots banging against one another. Clunking sounds generally happen when your vehicle is either going in and out of a pothole or going over a bump. Often, a clunking sound is created by an issue with the undercarriage of your vehicle. You could have a suspension issue, or something could be loose or dragging from the undercarriage.
A hissing sound is easy to identify. If you hear a hissing sound, you are going to want to pull over and stop your car.
A hissing sound may be coming from your cooling system for your HVAC; it could also be coming from under your hood due to your vehicle overheating. You can see if your vehicle is overheating by looking at the thermometer on your vehicle. This will let you know if your vehicle is overheating.
Finally, there is a howling noise. This is not a noise you want to hear coming from your vehicle, and it is a very distinct noise. When you hear a howling sound, that means something is wrong with your differential. The differential is what drives the speed of your wheels. If you hear a howling sound, you should stop driving and get help immediately, as it is important to have your wheels under your control.
If your car sounds like a stray cat that has gotten into a fight with another stray cat, it is time to bring your vehicle in for a check-up to figure out what is going on under the hood. Your vehicle shouldn't be making lots of weird noises; that is a problem and means your vehicle needs a little care and attention from a mechanic.