I have a cunning plan. I dont know if it will work, mainly because I have never had the opportunity to try.
Try putting a phone, with sound recorder running , as near as possible to potential sources of noise and see which one gives the loudest recording when you provoke the noise.
You could do the same with an assistant listening, but my method, if it works, does without an assistant and reduces the dangers of climbing under the car.
You can buy mechanics stethoscopes but these tend to be very localised in what they pick up.