Having some problems with my 07 plate 2.0 TDI (140) sportback A3, had the car 4 months, full audi service, next one is due next month. I was driving along over a week ago and noticed the car was making a strange almost kind of murmuring noise at 50+ mph, it sounded like it was coming from the rear of the car, so i thought the exhaust was possibly on the way out, had the car on a ramp and there aren't any problems from that perspective, so I did a few checks under the bonnet, noticed the coolant needed topping up, so I did that, the noise still seems to there and plaguing my mind a lot so iv been keeping an eye on things daily and noticed the coolant had dropped considerably. Had it checked out today at an audi specialist, they did a pressure test that didn't come up with any visual leaks, they're saying i need to have a carbon test done to check the engine internally for leaks, i don't have the creamy oil around the cap which is a sign of the head going. I don't seem to be having any problems with temperature, it sits right at 90. Does anyone have any advice on what else it could be? Does the noise from the rear and coolant loss seem related or two different issues? Any advice would be great!