I get the exact same problem. But I can hear mine from about 15 mph, although its hardly audiable at that speed. But the faster I get the louder and faster the tick gets. I thought it might be connected to the slight wobble on the speedo dial. But after watching it for a bit, i noticed they are not in time. There are more clicks to the wobbles, if you follow. I think, although I have to test this, it gets quiter if you have your heater on. I will test it tommorow if I can.
Paul