Have you checked the brakes? The scraping/grinding sound you describe sounds to me like your brake shoes (drums) or pads (discs) are worn out and you've got metal contacting metal when you apply the brakes. The reason it might sound louder when you turn left as opposed to right is that the left front wheel turns towards the driver when turning left and the grinding might be more easily heard then. Just a theory of mine.
I'd definitely start at the brakes when looking for the source of the sound.
