If you're a frequent driver, you'll likely be intimately familiar with how your car sounds on a daily basis. So much so that when a new squeak or rattle becomes audible, you'll notice it and it will annoy you. Most of these noises are fairly innocent - panels rattling or something not fitting quite right because of an extreme temperature change or pothole. My wife always finds it amusing when we're driving along and I'll turn the radio down and say "can you hear that?".
The worst case I ever saw of this was a few years ago. A friend of mine had this problem where his car developed the noise of an aircraft cabin call bell every 30 seconds or so, but only when he was above 70mph. It wasn't as loud as the 'bing' you hear when flying, but it was definitely there. It drove both of us to distraction but apparently me more than him. He ended up selling the car because he could never locate the source of the noise.