newish bike, around 3,500 miles. 12 speed dura-ace di2. cleaned and drip-waxed the chain last night, set off on a ride this morning. drivetrain was whisper quiet, truly quieter than the tire noise until approx 10 miles into a 50 mile ride, when i started hearing a regular ticking.
the ticking sounds like it's coming from the bottom bracket / crank area. it occurs once every time the left crank passes the front (9pm?) position. doesn't occur while pedaling backwards, doesn't occur when ghost pedaling (no load, slower pedaling than the bike is going.) it's not dependent on which ring in front or which cog in back, although the sound varies a bit depending on the exact condition and most especially the load. it's most noticeable riding uphill at slow speeds with high(er) power, a completely metronomic ticking in tune with my cadence.
there is no visible contact being made at the front, cranks look perfect, can't be pedals since it happens at the same point every time regardless of pedal orientation, there is no wire end on the fd to be making contact, careful inspection shows nothing making contact anywhere. don't see how it could be chain or cassette related since it happens once around the cranks, not once around the cassette or chain. no signs of cracks in the frame. it did start after a fairly misty and hard 10 miles, but nothing out of the ordinary.
mp3 file here - can't upload an mp3 as an attachment, unfortunately!
ticking sound mp3
any suggestions? i'm guessing this is going to be a shop fix but curious if anyone has any ideas.