Warbling Sound ?

[ARCHINSTL]

OK - this may be for the birds, but - despite a Search, I've not found this sound mentioned by anyone...

This is not a 'chirp,' but more of a slight 'warble.'
It has been extremely intermittent - by that I mean from occurring days apart to weeks apart.
The duration has been from a split second to possibly only two seconds.
It has occurred upon slight acceleration from a stop - or slight slowing for a stop - or turning into a street at modest speeds. I've not noticed it during hard acceleration (like fast entry onto a highway) - or at highway speeds (well, detectable above a T4WD's normal tone tumult at speed anyway...).
It is not loud - just noticeable. It seems to be coming from the engine bay. It does not seem internal to the block.

It seemed logical that it was from some kind of rotating device, like the distributor, the water pump, the PS pump, or the alternator. But - nothing seems amiss or making funny noises when touched at various RPMS. I checked the alternator with a multimeter and the output is fine; I had suspected (hoped) it was its bearings, but nothing seems amiss.
The PS pump is OE, the water pump was new by PO 13K ago, the dist was a reman 11K ago, and the alternator looks like OE.
The pump/alternator and PS belts are fine and not loose (no AC stuff).
I dunno if the clutch and its workings could be suspect here, but nothing seems different upon engagement or disengagement.
I also checked the wheel stuff for anything dragging or ensnared, but nothing.

The frustrating part is the extremely infrequent occurrence, the varying very short periods of duration, and the appearance during different (gentle) types of operation.
Thanks.
Tom M.

[Petros]

check your lug nuts. 80 ft-lbs each.

[ARCHINSTL]

Will do tomorrow - that was NOTHING I had considered. I actually always use a torque wrench on them, but to Owner's Manual spec of 76 ft-lbs. This is ever since some yahoos at a Sears store in Smyrna TN overtightened them and broke off two studs when I got Goldie.
Will report - Thanks.
Tom M.

[4wdchico]

I had a similar issue with a girlfriend's te71 'yota many years ago. It turned out that the noise was from the alternator pivot bolt being significantly loose and at certain engine rpm a strange cyclical noise would be generated. Since the belt was still tensioned the alternator performed fine. When I found the problem I had to replace the cast iron alt mounting bracket thru which the alt pivot bolt passed as holes had been worn oval in the cast iron by the alt pivot bolt.

[ARCHINSTL]

OK - Today I:
Tightened the lug nuts to 80 instead of the OM's 76 ft-lbs (none were loose at all);
Checked the alternator pivot and adjusting bolts - both were tight;
Removed the AC tension pulley and its long adjusting bolt & shaft from the alternator bracket. I had not removed
.....this when I removed the AC stuff last year - it was loose, but then it's been loose for at least 6 years;
Checked the X-member and steering rack bolts/nuts - all were at proper torque.

Since this was so darned intermittent - it will simply be a matter of seeing if it appears again. I will report back if it does.
In the meantime - if anyone has any other recommendations - FIRE AWAY!
Tom M.

[ARCHINSTL]

Following up on this...
Since doing the preceding - and nothing else - the warbling disappeared and has not recurred for these 5 months. I'm now convinced the sound was from the idle and isolated AC pulley vibrating or rotating when certain engine RPMs or vibrations encountered. When I removed it, it looked kinda rusty around its bearing.
Tom M.

[dlb]

i had been wondering about this! congrats on figuring it out!