This will give a high pitched squeal all the time, not just when braking and usually happens on disc brakes.
THINGS TO LOOK FOR
You will need to remove the wheel from where you think the noise is coming from and have a look around the stone guard. The stone guard is a guard to prevent stones from hitting the disc brake rotor. What you should find is a stone. These noises just come on out of no where and they usually come on when you have been travelling on an unsealed road.
You can do it yourself or your local auto club can come out and look at it for you, or your local mechanic. The cost is around $10.00 for an inspection..
This article is found in the Virtual mechanic CD Rom
You can download it for the price of a latte, but you will learn not to buy a lemon
By Darren Gow-Brown, Melbourne Australia ©2009