An automobile was never created to be a silent machine. In fact, it is perfectly normal for it to make some noise as you are driving down the road. It is normal to hear the wind whistle against the radio antenna; and it is normal to hear the tread of your tires hum as they grind against the asphalt you are driving on. There are, however, other noises, including scraping and hissing, that should not be ignored or written off as "normal".
It should not sound like someone is dragging their nails across a chalkboard when you brake or accelerate. In fact, chances are pretty good there is something wrong with your accessory drive belt. The belt could be loose, cracked, or simply worn out. Unless the problem is that the belt is loose and you can secure it to make the noise go away, the only other option is to replace the belt with a new one.
If you hear a scraping or grinding noise while you are braking, it is also possible that the brake pads on your vehicle are worn out and need to be replaced. Naturally, this is a repair job you need to get accomplished quickly as worn out brake pads will make it more difficult for your vehicle to stop when you press down that brake pedal. Continuing to drive on worn out brake pads can also cause damage to the rotors and result in them needing replaced as well.
A hissing sound radiating from the engine while you are driving and/or after the vehicle turns off could be a sign that the vehicle is overheating. It could also be a sign that coolant is leaking from your vehicle's cooling system. You should start by checking the temperature gauge on your vehicle to see if the vehicle indicates that it is getting too hot. Naturally, you should not continue driving while the vehicle is overheating. If you should see smoke emitting from the hood, you should stop the vehicle and distance yourself from it immediately.
After you stop the vehicle and any smoke has dissipated, you can inspect for any evidence that there is a coolant leak in the radiator, engine, or hoses. A sweet smell is a sure sign of leaking antifreeze. Make sure you do not try to open the radiator or the cap on the coolant reservoir until you have given the vehicle time to cool down. You also should not add any additional coolant until the vehicle as cooled down.
As you can see, your vehicle making a scrapping or hissing noise is not the end of the world. It's only going to get worse if you ignore it, so take your car in for service at a repair shop like Oak Hollow Tire Car Care Center Inc.