Sound of Rushing Water
When you hit the brakes and come to a complete stop and hear the sound of rushing water under the hood, the brake fluid is probably leaking. Leaking brake fluid means your brakes are likely to malfunction soon, so you might want to get this checked out.
Strained Cranking Sound When Idling
The water pump might be on its way out. The cranking sound could be the belt rubbing against the water pump bearings, which are likely suffering from a weakened seal.
Upon making a turn, you might hear a squealing sound from the steering column. The power steering fluid might be low or leaking, causing a lot of friction.
This is an indication of the brake pads wearing out. The grinding sound is there to inform you that pads are getting too low. After too long, that grinding sound becomes a real issues as bare metal rubs against and wears down your rotors.
Squealing at the Slightest Turn
If you hear a squealing sound even when you slightly turn the steering wheel, then the problem might be a loose belt. The power steering fluid is probably not the problem if the wheel turns easily.
Sizzling Under the Hood
Sizzling under the hood means a fluid is touching the hot engine. This could be an oil leak, a transmission fluid leak, or a coolant leak and you will not know what the source is unless you check.
A loud "boom" sound coming out of the tailpipe could be the result of the catalytic converter not properly regulating the fuel system. Beware, a faulty catalytic converter could very well cause a fire if not fixed.
Knocking and Pinging
These sounds are also connected to the fuel system. Generally, when the octane of the fuel is too high or you have simply made the wrong brand selection of fuel for the car, the engine is going to knock.
Metal on metal scraping could be indicative of something being out of alignment. The scraping sound is literally two components rubbing on each other. The severity of the scraping is going to depend on what parts are affected.
Rattling is often a loose muffler. The muffler could eventually fall off the car if this problem is not corrected.
Tapping in the Engine
Your engine oil is probably low, so unless you want to see the car turn into scrap metal, add more oil. Check the oil afterwards because you may very well have a leak, an issue that should be fixed immediately.
Squealing and Dragging from the Tires
Yes, you guessed it, if you hear a squealing sound from the tires, then chances are great that one or more of your tires is low or outright flat. The car may drag a bit on the ground and slow the vehicle due to the inability for the tire to do its job.
Hissing Under the Hood
Your coolants are either leaking or dangerously low. Either way, the hissing is likely the sound of your car overheating. One quick trick is to turn the heater on to help pull heat away from the engine. Use this trick on your way to getting the problem fixed and NOT as a long-term solution.