I live down a gravel lane.. And when im driving on it.. It sounds like a knocking noise coming from the left front wheel. Out on the road its fine. Even hitting bumps in the road you dont hear it. Only on the lane. Anyone know what this might be? I am not very mechanically inclined. I mean if you tell me what it is i can find out how to fix it but I cannot determine it or even know what to look for. Drives straight as an arrow.