On Fri, 23 Nov 2018 11:59:31 +0700, John B Slocomb wrote:

On Thu, 22 Nov 2018 16:05:54 -0800, Joerg
wrote:

After installing a new Sunrace 40-11T cassette (minus one cog), a new
chain and a new rear derailer the road bike can now climb hills much
better. 40T as biggest cog versus 32T before. Woohoo!

However, on the middle and three larger cogs (it's now a 7-speed) there
is a distinct vrrrt .. vrrrt sound when under heavy load. Maybe from the
chain because with a derailer setup it'll never run 100% straight. Hard
to say. The noise appears briefly twice per pedal crank rotation and
always on the power strokes.

The chain is a KMC Z50 that should be suited for 7-speed and I looked,
it doesn't rub against a neighbor cog. Maybe a "teeth exit grinding"? On
the 3rd cog from the largest it's really weird because that has an
almost perfect chain line when on the small chain ring up front.

Anyone heard that before? Can it simply be ignored? Or maybe it'll go
away over time?

I've had a noise from a front derailer due to the chain rubbing on the
derailer "cage".

Sounds like some distortion somewhere under load.
Does something need a clean; both pedal bearings, the bottom bracket, the
chain ring bolts(clean and tighten), etc

The only other sound maker I've come across rarely is chain rubbing on
chain from too much wrap in the rear derauiller or chain rubbing on tyre
from great sag/too little pick up in the rear derauiller but the fact
that is across four cogs is would indicate that it isn't likely.