Odd "Warbling" Noise

[ARCHINSTL]

This started a few weeks ago.
It is not a squeak and not quite a "chirp," but more of a "warble." It seems to be from the DS in front of the panel, whether in the engine bay or the instrument panel.
It is intermittent, meaning every few seconds, with quiet spots of perhaps 15-30 seconds and sometimes a few minutes. It is not loud.
It is present when in gear, or coasting out of gear, or even when coasting with the engine off - so that would seem that it is not drive train related - and it is not present when stationary and the engine running at various RPMs. The intensity or frequency does not at various RPMs on the road.
It is present whether on "rough-ish" concrete roads and on smooth asphalt surfaces (perhaps just a little less frequent on asphalt).
I've not had occasion to go on the highway (will tomorrow), so dunno its reaction at speeds above 40 MPH.
My current thought would be the speedometer cable - but the speedo arrow is rock steady as always, with absolutely no wavering.
I perused every single thread here about speedo and cable woes, but have not found anything at all similar.

Short of advice, when it ever stops raining here, my plan is the remove the instrument hood, move the cluster back enough to disconnect the cable and see if that eliminates the warbling. I'd rather not try removing the cable from underneath, as the gravel driveway is just a swamp.
IF it disappears when the cable is unhooked - can lube be dripped down the sheath from the speedo end, or do I need to remove it from the trans end?

Any other thoughts?
Thanks,
Tom M.

[Jonymoto]

Tom, you will be able to drip oil down the cable from the instrument end. Last time I removed my cluster (to replace an instrument light bulb) I used bicycle chain oil as it flows very easily and had Teflon in it. But you can use any oil that flows. It's a bit of a pain reconnecting the speedo back as it is a bit on the short side (for RH drive Tercel).

[ARCHINSTL]

A-HA! I still have several oils from my days owning a bike shop: Tri-Flo, a light oil for brake/gear cables, and Phil Wood Tenacious Oil, a more viscous product.
Thanks,
Tom M.

[Jonymoto]

Myself, I'm what they call a MAMIL here (middle age man in Lycra), so I do a bit of cycling at the weekend (mostly on road bike) just to keep fit. So I keep plenty of chain oil. I also use them on the cables.