This is a re-post. I tried earlier, but it didn't show up; apologies
if it shows up twice.
I've got a full ultegra triple - 9 speed setup (rear derailleur is
durace though) . When on the middle and small chainring it is smooth
as silk, but when on the outer chainring, it feels like it is
vibrating and is really loud while on the outermost 2-3 cogs in the
rear. (problem starts with 3rd smallest, get worse as they get
smaller - therefore worst on smallest).
When I pedal by hand on the repair stand, I can feel tiny bits of
resistance as if the chain was catching on rear sprocket teeth.
The best I can desribe it is a very pronounced, loud and "coarse"
vibration - the vibration seems to be identical to what the teeth on
the rear sproket would make as the chain passes over it. It is not the
frequency of the front chain wheel cycle, but seems to be the
frequency of the rear sprocket, if that makes sense. If I were to
imitate it, I would whrrrr my tongue on the roof of my mouth.
I know it is NOT: chain noise on front derailleur cage. The chain
does not rub on the front der. cage in any normal (not cross chained)
combination.
I also know it is NOT the noise that is caused by rear derailleur
cable adjustment. I have fiddled with rear der. cable adjustment with
no effect on this particular noise. I am familiar with the sound and
solution of the rear derailleur cable needing adjustment. I have it
adjusted so that shifting up and down the rear derailleur with normal
combinations of front chain rings is very crisp and smooth.
It ONLY happens on largest front chain wheel and smallest 2-3 rear
sprockets. Obviously, this is a "normal" gear combination.
It could be rear derailleur alignment. If so, would that explain this
type of noise - or why it only happens with large front chain wheel
and rear smallest two or three sprockets?
Is there an "idiot's guide" to fixing rear derailleur alignment. I
don't believe I've ever correct a bent or mis-aligned rear derailler,
but understand the principle of alignment. I don't want to just start
trying to bend anything!
The drive train is very smooth and quiet on all other "normal" (i.e.
not cross chained) combinations of rear and front gears. As I said,
shifting is clean and crisp on all normal combinations.
Thanks in advance for any help or pointers!