When your car is acting up in any way, you can often determine where to start looking for needed repairs by the sound you hear. Car problems might cause popping, grinding, howling, and other noises that you know you shouldn't be hearing from under the hood. Knowing what these sounds might indicate can tell you what to share with your mechanic, and what you might be expecting by way of repair bills.
If the engine seems to pop when you change gears, this often means that there is a dirty transmission filter or dirty transmission fluid. The gears are not moving smoothly as you change them, so you hear this popping sound. If you hear the popping sound when you're driving straight, this often indicates a rusted tie rod. This is a long piece that connects the tire to the steering column; when it rusts or is bent, you'll hear this rod pop as it moves back and forth into position. There may also be broken or missing lug nuts on the tire's rims, and this causes the connections to pop as they go back and forth with each rotation of the tire.
If you hear grinding when you apply the brakes, the brake pads are probably worn down and need changing. This can also mean a worn down rotor, or one that has a significant amount of damage including grooves and even chips. Rotors can be turned, which is when they're polished to be smooth, if they're thick enough; otherwise, they need changing. If you hear the grinding noise when you turn the wheel, this often means that the car is not getting enough power steering fluid and the gears of the steering column are grinding against each other. This could indicate a leak in the system or a worn power steering pump.
Howling or sucking air
If you hear a howling sound or what sounds like the sucking of air while you drive, this often means that there is damage to gears and that air is getting through them. Note if there are other problems that could indicate which gears; if you have a hard time steering, this indicates the steering column and its gears. If you hear the howling when you turn a corner, this usually means the differentials, which are gears connected to the tires and which allow them to turn at different speeds when you turn. Usually these gears need to be changed when you hear these sounds.