I can hear a dull clicking sound when I ride. Lower pitched than, say, a piece of rock being kicked up by the front wheel and hitting the (aluminum) frame. Each click is almost like a creaking but of a much shorter duration (maybe a few milliseconds at most). The clicks come in irregular groups. This started a few days ago and it happens every few minutes during the ride, then it stops for a little while and starts back up again. The problem only occurs when pedaling.
It seems to be coming from somewhere around the bottom bracket or drivetrain. I put the bike on my stand yesterday, tried out a few gear combos I most commonly use but I couldn't reproduce it.
For now, it doesn't affect the ride.
Any ideas what I should look into?
Bike is an '07 Specialized Allez Double.