A bruit is a sound which identifies turbulent flow of blood. Although this is not "normal" it may be of little clinical significance depending on the rest of your physical exam findings. However, always pay attention to your body and never be afraid to get another opinion. Immediately seek care if you have changes in urine and/or severe pain.
If it isn't concerning your doctor then try and relax about it there may be a completely different reason for the noise and they just haven't done the right test yet to let you know exactly whats causing it. If it is truly concerning you set up a consult with the doctor and have them explain it better.
Bruits over the kidney are a sign that you have atherosclerotic disease of the renal arteries. This causes stenosis and can cause problems like hypertension and kidney failure. It is also a marker of systemic atherosclerosis. I would see the doctor again to minimize your systemic risk.
If the doctor hears a bruit when listening to the area of your abdomen near your kidneys, you may have some stenosis of the arteries leading to the kidneys. However, this is more likely to cause hyptertension than it is a problem to the kidney itself in its early stages.