[T3] A noise I've never heard

[timothy kuehn]

Howdy.

Looking for some second opinions, before I go tearing stuff apart...

I have an engine-area noise.  High-pitched, non-percussive, seems like more of a rub/scrape than a knock/slap.  But rhythmic and quick, so it sounds knockish when you first hear it.
Best I can describe the noise is a sharp 'Ch' sound.  Almost like an angry blue jay.
It is RPM dependent, and most apparent at idle - it either disappears at higher revs, or at least doesn't increase volume with RPM, therefore drowned out by exhaust and normal valve sounds.

Noise has no effect on power.  Oil good, valves good, pushrods good, nothing loose on tin, heads, case, manifolds, plugs, etc.
There is no trapped blue jay.  I checked.

Noise happens with every rev, not every other - could this eliminate or indicate anything? 
What do failing rods, bearings, dying valves, etc. sound like?  I've been led to believe these noises are bassy and unmistakeable.  

I've had inner fan shroud bolts work loose before, and make that distinctive stone-in-the-lawnmower racket.  I know that noise.  This is not that noise.  But it could be similar?  Like the fan rubbing/striking something stationary, as opposed to little pieces flying around in there?  
Listening to idling engine with a dowel, I cannot really locate the noise to the fan shroud.  But I'd be thrilled if this noise were fan-related, and not internal!

Bent cooling fan?  Do they get bent?  Do they get loose?  Could the crank walk around, therefore shrinking the clearance between fan and inner fan shroud?  Could the inner shroud warp, and make contact with the fan?    If this has ever happened to anyone, could they kindly describe noise and symptoms?   

Anyone wanna justify a more dire diagnosis, like 'this noise is certainly a cooked bearing, stop at once!'  ?

Thanks!

--Timmy
'72 square
Venice, CA







   
 		 	   		  
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