rear derailleur squeal

Charles M said:

Question about what to adjust: My rear derailleur squeals
when I shift to higher gears (but shifts OK, otherwise). It squeals
all the while I'm in a higher gear. Lower gears seem to be free of this.
Also, if I pull up slightly on the index shift lever (i.e. lower gear
direction), the squeal goes away.
Note that its OK in other respects, doesn't travel too far or
cause the chain to fall off.

CMM

I'd think this indicates that the pulley/jockey wheels through which the chain
path rides need to be lubed. Depending on the RD model, it can be very simply
to remove these, clean them, lube the bushing, and re-install. Also, you can
try hitting them with some spray lube which may be easier still. Some folks
replace the standard issue ones with sealed bearing units.

Charles M said:

Question about what to adjust: My rear derailleur squeals
when I shift to higher gears (but shifts OK, otherwise). It squeals
all the while I'm in a higher gear. Lower gears seem to be free of this.
Also, if I pull up slightly on the index shift lever (i.e. lower gear
direction), the squeal goes away.
Note that its OK in other respects, doesn't travel too far or
cause the chain to fall off.

CMM

In my experience this usually means the jockey wheel needs to be oiled.

Charles M said:

Question about what to adjust: My rear derailleur squeals
when I shift to higher gears (but shifts OK, otherwise). It squeals
all the while I'm in a higher gear. Lower gears seem to be free of this.
Also, if I pull up slightly on the index shift lever (i.e. lower gear
direction), the squeal goes away.
Note that its OK in other respects, doesn't travel too far or
cause the chain to fall off.

CMM

Pulleys off, clean, grease, reassemble...