12/7/15 4:23 AM

My wife likes flat bar road bikes, and the most recent one that I built up for her earlier this year, I fitted XTR 9000 shifters, RD, cassette and chain. From the first time she rode it after the new components were fitted, she complained that the drivetrain would intermittently be quite noisy, particularly when climbing hills. I could confirm the noise on the workstand - it sounded as though the RD was sometimes resonating, leading to a buzzing noise as though the jockey wheels weren't properly aligned with the rear cog (they were correctly aligned), and the noise was related to crank speed, becoming more prevalent at a higher cadence and pretty much disappearing at a slow cadence. Engaging the clutch on the derailleur seemed to reduce, but not eliminate, the number of situations when the noise appeared.

After a fair bit of experimentation - replacing jockey pulleys, varying the position of the B screw to place the top pulley nearer or further from the cogs, and swapping the original XTR chain for KMC chain, none of which made any difference, I finally replaced the XTR RD with an XT M8000 when 11-speed XT came on the market. Problem instantly solved! The noise has never appeared with the replacement derailleur.

Anyone else come across such a problem? Have a solution? At the moment I have a rather expensive RD gathering dust...

12/7/15 7:59 AM

Any chance the XTR9000 had been damaged and the pulley cage was mis-aligned? It wouldn't take much of a bend to make it run noisily.

12/7/15 2:57 PM

No, I checked the pulleys and derailleur cage, and they were in the same plane as the cassette cogs. Plus the problem was intermittent - she could be riding along with the gears sounding quite normal, and then without changing gear or touching anything, the buzzing would suddenly start, and then some indeterminate time later it would as suddenly stop. Which is why I thought it was some sort of resonance problem.

I could try fitting the derailleur to another bike to see if the problem happens there, but AFAIK Shimano 11-speed MTN is compatible with nothing but itself, and the only other bikes I have with 11-speed are using SRAM and Campagnolo road shifters.

12/7/15 4:07 PM

sounds like a pulley bushing... did you pull the pulleys and see what is or isn't in there grease and or water/oxidation wise??

Does the sop pulley float properly?

12/7/15 8:08 PM

Being XTR, both top and bottom pulleys had sealed annular ball bearings. But one of the things I tried when attempting to fix the problem was to replace the pulleys with a set off an unused XT derailleur that I had in my spares collection. The XTR pulleys when I removed them felt and looked fine, as did the XT replacements, but the problem persisted as before...

Float was fine on both original and replacement top pulleys.

12/9/15 6:12 PM

I'm going to have to go with Sewer Snoids (Gilbert Sheldon reference, I think).