Moishe

Kinda new (2,000 miles) Domane SLR6 with Bontrager Paradigm Comp clincher wheels. Clicks once per wheel revolution while peddling, but the odd thing is that the clicks go away when I shift down to the next larger cog and return when I shift back to one of the middle cogs. I do solemnly swear that the clicking is in time with the wheels and not the crank, that the spokes are all equally tensioned, that the valve stems are screwed down snugly, that the magnet is not touching anything, and that cleaning and lubing the freehub (though without replacing the bearings) had no effect. Help me and I'll buy you a high-alcohol-content IPA.

practical

I had a similar issue - a clicking noise when I pedaled. I couldn't recreate it on the stand so I couldn't figure it out. Brought it in to the shop and they found the bearings in the bottom bracket were shot and replaced them. Problem solved. But your bike seems to be too new to have this problem.

Unca_Sam

Drivetrain noises are F - U - N to diagnose! A little more detail might help. Can you pinpoint where the wheel clicks in the revolution? I'd want to say you have something stuck to your tire, but you say it's only under pedaling. I wouldn't be so quick to say it isn't your rear mech, since that by definition is coupled to the wheel as long as you're pedaling.

Since the cassette is external, look over the cogs carefully, maybe you have something stuck or bent that's hitting the frame once per revolution.

Can you put it in a repair stand or trainer to listen closer? What hubs are you using?

Moishe

Thank you Mr. Practical. I should have made this more explicit--the click sound occurs once per WHEEL revolution while I'm pedaling, so it can't be coming from the bottom bracket, but I am holding out the hope that the cause is the rear wheel bearings. I'll look for you at the next Kelly Brush Century ride.

Moishe

Thanks, Mr. Sam! I'll obsess over the wheel location of the click on this afternoon's ride.

dsbrantjr

Check to make certain that the lock ring is clamping the cassette properly and that there are no missing/misplaced spacers. It is possible that the cogs which are clicking are the un-attached ones and the quiet ones are fastened together on a carrier. Also check to be certain that the rear derailleur or its shift wire are not hitting something like the magnet or other wheel part in certain gears and not others.

Crankycrank

I once had a wheel magnet sensor innards break loose. This made the once-per-rotation click most but not all the time. Tried gluing it back together but no luck. A new sensor solved the problem. Try tapping the sensor to listen for loose parts or take it off. Open up the battery cover as well and check inside. A long shot but worth checking.

delbiker1 

Another set of ears riding with you to try to pinpoint where the noise is coming from might help. It is really hard to figure out where a noise is actually coming from while riding. Too much other noise and not able to focus long and hard enough to figure it out for sure. Those kind of clicking noises can drive you crazy.

Moishe

Well, after fifty miles today, I determined that the clicks occur once per wheel revolution only when I am pedaling in one specific cog, the fifth largest one (out of 11), in either chain ring.

More research tomorrow.

jadocs

It's probably your skewer or through axle. Remove, clean, lube and torque through axle to spec. If QR, make sure it's tight.

OneIsAllYouNeed

Derailleur hanger straight?
Cassette lockring tight?
Cassette tooth bent?
Rear shifting tuned perfectly?

Unca_Sam

Hanger rub is continuous, not what OP described.
Messy shifting sounds like messy shifting, not a once per wheel rev click.

Tooth bent? Lockring loose? Maybe. A bad press link job or missing link would be every chain rev. Bad pulley bushing/ bearing is usually a rattle and easy enough to diagnose. Debris in the cassette could be hitting the chain only in the 5th cog, but that's easily checked.

Unca_Sam

Moishe,

I want to confirm that your bike is using the Di2 system. I have no experience with it, though someone may have.

I noticed Di2 rear derailleur clicking under power search results on other forums, sadly with no posted solution. Those posters tried reindexing, other cassettes and wheels, new hangers, but the closest i saw to a fix was top swap for the right cassette or file the sticky cog tooth so it doesn't catch.

Here's a similar thread:
Clicking/ ticking Ultegra 6800

OneIsAllYouNeed

A bent hanger can definitely cause bad shifting in one (or a few cogs) anywhere on the cassette. In this case, it’s likely that the chain is hitting a cassette shift aid once per wheel revolution. On Di2 or eTap, the shifter can be microadjusted to quiet that cog. With mechanical derailleurs, the best bet is to straighten the derailleur hanger.

Moishe

Clicking mystery solved! Replaced by a market mystery!

It turns out that the clicking was caused by the space between the fifth and sixth largest sprockets on my Ultegra 11-speed cassette being narrower than between all the other intersprocket spaces. The built-in spacer on the 20-22 tooth combo unit (the fourth and fifth largest sprockets) was too narrow by a millimeter or two. When I replaced this combo unit with the 20-21 tooth combo that originally came on my Dough-main slr6, the intersprocket spaces were equal and the clicking was gone.

This raises the market mystery. I can’t imagine that Shimano’s quality control is poor enough to produce this defective two-sprocket combo unit. Are there such things as counterfeit Ultegra 11-speed cassettes out there in the Gray Market? I wouldn’t think that a counterfeit manufacturer could make enough money peddling bogus cassettes. Some Taiwan e-Bayer is selling these 20-22 tooth units, which are otherwise hard to find—is there a chance they’re genuine?