I was driving recently and heard a strange noise coming from my front wheel; I thought maybe I'd caught a stick or branch, and the noise seemed to go away every now and then...
I gave it a cursory look and couldn't see anything obviously wrong - although I am by no means a mechanic.
Then the noise started to get worse and louder, so after a week or so I took it to the mechanic. Turns out one of my wheel bolts was about to shear off, and there was a chance my wheel could have come off at any moment!
It cost less than $200 to repair - a small price to pay when you consider the alternative.
The moral of the story; small noises bear investigation by experts - it could save your life!