Couple of posisbles -
Thrust bearing is a possible option - normally this would be consistent in all gears though and increase in noise as engine speeds increase, so might not be. Does sound like a drivetrain issue rather than an engine related problem.
Front wheel bearing - these make weird kinds of noises as they wear out - jack the front of the car up and see if the wheel has excessive play in it. Under load these will make noise and whilst coasting can be quite - might match your problem, also your kilometers would fit about right for the first wheel bearings needing some replacement.