1x AXS drive chain makes click noise only in highest gear
 

This is my first post on the forum and it turns out to be a help ticket..

I recently put together a new 1 x bike, all parts are new and SRAM RED AXS, now here is the weirdest thing.

If I shift to the highest gear, the crank seems to make random unpredictable clicky noise and it doesn’t matter how fast I ride or how much power I push, it’s not in any regular interval and it’s not a squeaky noise, more of a loud clunk noise a torque wrench make and I can feel the vibration from my feet, so this could also be the chain or the derailleur or the cassette.

If I’m using any other gear, at heavy load and full force standing up hill the whole drive train makes no noise and is completely silent.

I also can’t reproduce the noise in a bike stand when the drive chain is spinning free or with moderate brake resistance, so the noise is only there when I’m riding.

From the description above I believe the noise isn’t from the bottom bearing, seat post or pedal, it also doesn’t make sense it is the crank as the crank is a none flex object. I also checked my cassette and ensure there is enough space between the last cog and the frame so it’s not the chain hitting the frame.

At this point I’m thinking to mount a go pro camera on my seat post looking at my rear derailleur and chain in high FPS and see what the hell is going on, but any other insight is super appreciated.

Some 1x setups have chainline issues.

If your bike frame is spec'd with a road group but uses an MTB hub, the hub chain lines are different. Road is 41.5mm while MTB is 44mm. This pushes the chain 2.5mm further outbound and can create problems like loud, clattery drivetrains, chain drops, chain slips or it can decrease shifting performance.

Have a look at your chain line and see if it is the problem or perhaps a contributing factor to the problem.

Good luck.