I've experienced a similar noise.
It would start at approx 20-30 mph and the 'ticking-interval' would increase with speed.
Turned out to be the errr.. don't know the english word for it! -'The small odometer you can set to zero by pushing a button'. It had gotten stuck somehow when i pushed the button at my last refuelling. I pushed the button a couple of times and i went away..
Never criticize someone until you've walked a mile in his shoes. That way, when you do, you're a mile away -and you have his shoes!
'86 300E optically converted to '95 E300 (Sold)
-Blauschwarz on silver
-17" AMG & 15" AMG for winter