The car started to make a metal scrapping sound out of the blue. It is quite loud. And it is only when I am in drive. If in reverse or braking it does not make the sound. If I pull over and turn off the car. Then turn it back on. It sometimes stops making the sound. What is causing this?
My car has 175000 miles.
My car has an automatic transmission.
There are really only a couple possibilities: if the noise started "suddenly" or abruptly, as you describe it, you may have picked up something from the road that is somehow "lodged" somewhere rubbing a wheel, shaft (axle), or other rotating part. That possibility also could include something metal ON your car that has moved out of position (gotten loose) and is rubbing on a rotating component or suspension.
The second possibility is you have a part failure in the braking system (possibly worn out pads, but what you are describing is not consistent with that) or an internal part failure potentially in the transmission, torque converter, differential, axle (CV joint) or similar "moving" part.
For the first possibility, you might be able to track it down using a visual inspection but you have to get the car pretty far up off the ground. The second possibility would involve applying wireless "chassis ears" to various parts of your car and driving it to pinpoint the exact "area" (or component) which is generating the noise.
Once the area is pinpointed, it is fairly easy to go from there and identify the exact problem. Prior to using tools such as chassis ears, of course, it is possible that YourMechanic can pinpoint the noise just based on actually hearing the sound and its apparent location. Sometimes noises are so "diffused" throughout the vehicle that chassis ears make the diagnosis much more efficient though.
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