1997 Toyota T-100 Timing Belt too tight

Anyone had a problem with a timing belt becoming too tight?
I have a 140,000m T100.
It had a new Mitsuboshi belt, Aisin pump and new Idler and Tensioner @ 95K. (I bought this truck @ 140K)
Motor was very quiet when cold BUT got progressively more noisy when hot.
Sound was very metallic - a sort of rattle, scraping noise. A noise in fact just like a dry worn-out bearing.
Sound was apparent front and center.
Removed radiator fan and bracket, all V-belts (propped AC pump etc. To the side) and the top cowling to get better access.
Ran the motor like that.
Harbor Freight mechanics stethoscope used to pinpoint noise.
Noise NOT from water pump but both pulleys very noisy.
Replaced both with no change. New pulleys also very noisy when motor hot.
Belt looked good and still had all markings.

Following a further removal of the belt to inspect the idlers etc. Noticed something strange when installing tensioner when the motor was still warm. Could not tighten down the two 12mm bolts by hand.
Tightening with a wrench was necessary just to get the tensioner flange to seat.
At this point, the belt had so much tension, it was possible to 'play a tune' on any straight sections between pulleys etc.
Also, the install pin in the tensioner piston was completely loose - the piston was completely 'bottomed out'.
. Removed the belt again and compared it to a new one on the bench. Both side by side laying flat, gently flattening out each end to get visually equal radius. (Not too flat!)
After careful 'eyeballing', could not see any difference between them but could feel the new belt was more supple.
Put the new belt on and was able to tighten both tensioner bolts by hand before torquing then up.
When the install pin was removed, a noticeable movement of the tensioner pulley was observed.
When the motor warmed up, just the slight 'sewing machine noise' of the lifters was apparent. (Yes. Also done the valve clearances in all of this!)
So. Have to presume that the old belt had maybe 'swelled' and was a little fatter - and as the back of the belt contacts three pulleys, any additional 'fatness' would effectively make the belt shorter.
No oil or coolant was leaking so I cannot attribute any swelling to that!

I emailed MBLUSA. COM (Mitsuboshi) and invited them to comment and offered to forward the belt to them for analysis. Unfortunately, I have not heard back from them.
I would be most interested to know if anyone else has experienced this problem and what the cause may be.
Thanks for reading