... That reminds me of an ol Peugeot 404, my first car. I put a roof rack on it and it developed a most pronounced wind howl. In my ignorance, I diagnosed the noise as coming from the rear end. One of many lessons at Ye Ol School O Hard Knockers!

My 70 owner's manual says to use engine oil in the M41. ATF is a lot thinner than engine oil. I'd switch to RedLine 30W synthetic. If you notice a change in noise after changing to the thicker oil, then you've located the source - or at least one source.

I'd consider other easier stuff first, before ripping into the M41. Driveshaft U-joints will vibrate and growl before the needles fall completely out. Also, ds center support bearing is suspect. So are rear end input bearing and wheel bearings. (Diffy gear noise is not constant and changes w/ throttle-on or throttle-off.)

Good luck!
Al