Identifying Chirp noise

[Roberts280Z]

This Z hasn't been driven in over 10 years.  I started recovery by oiling the cylinder walls and cranking by hand.  I eventually graduated to actually running it.  There was a sporadic 'chirp' noise, which went away quickly.  After some A/F tuning, I got a smooth idle, allowing a trial run around the block.  But then fuel tank issues added a 2-month delay.  Yesterday when I started it, it began well enough, then the 'chirp' noise returned and stayed.  I then noticed that the noise occurs even when only cranking - occurring on every second revolution.

I might assume this is valve related - perhaps a bent stem or otherwise sticking valve.  Vacuum is dead steady, but I assume that only 'sees' intake valve problems.  I haven't had the valve cover off yet, which I should do anyhow to check lash.  But for this noise, I don't know what I would look for without removing the head.  The last time I tried running the engine without a valve cover 20 years ago is still evident on my garage wall!  Maybe I can get away with merely cranking with the cover off, but I still don't know what I would do, other than to try to localize the sound.

Curiously, the only relevant search hit on this forum for 'chirp' noise turns up a question on the oil pump.

Does anyone have an ear for this type of noise?  Perhaps I could post a short audio/video file.

Thanks in advance,

Robert

[siteunseen]

It could be the water pump or the distributor button too. Get a short piece of garden hose to use a stethoscope and you can get really close with that.

[Roberts280Z]

I use a 3' piece of vacuum line stuck in my ear for that.  I had gone over the valve cover area to no avail.  But I'll widen my search.  Thanks!

[Zed Head]

You can run the engine for a short while with the belts off.  If the noise goes away it's something a belt was turning.  Or the damper pulley (the drive pulley).

AC idler pulley bearings are known to go bad and make noise.

[Roberts280Z]

Thanks for the suggestions.  Of course today, the chirp has disappeared all by itself.  I'll continue cautiously.