I'm thinking this is a diesel thing, but not totally sure. I thought I've heard it coming from some other diesels before. No foot on the accelerator, just letting it coast, I can occasionally hear a faint clicking when I am close to a guardrail, or cars, or anything else the sound can bounce off of. Just wondering what this might be. It happens much more than I notice it I'm sure, but I've only noticed it a handful of times since I got the car.