Howdy,

If the supply voltage to the oscillator changes, even though the
tuning voltage is stable, it may chirp or pull.

If the change is slow look for thermally induced changes like
You may not be able to feel this change with a finger. Applying
a bit more heat to suspected parts might indicate the culprit.

Also look for changes in the voltage on large capacitors. It
wouldn't be unusual for bias voltages to change when the oscillator
starts up. An extreme case of this is squegging.


73,
Grumpy