shakey speedo and tach

["Mark S. Lepore, MD" <Sirmoog@ix.netcom.com>]

Listers:
Another question for the common wisdom.
Both my speedo and tach needles "jump" while operating.  In other words, they
don't point calmly, but oscillate or vibrate around whichever number they are
trying to point to.  I've noticed that slight manual manipulation of the tach
cable can either improve or worsen the condition.  I've not tried this with
the speedo, but I know both knurled nuts are very tight on both gauges.
Any thoughts?
Sirmoog