Thank you all for the feedback. I'm pretty sure the tensioner is stripped. Turned at least 15 turns and no change on the pointer or in the slack. I put a tiny bit of belt dressing and that seems to have taken the shrieking noise away.

Will look for the parts and probably do a change over. I do understand the difference between the american alternator belt's simplicity in design and maintenance (being able to adjust it by swiveling the alternator), but then again, you gain vibration.

On the 300e, this might be the reason why the engine is so smooth and efficient balancing of torque. Ridiculously smooth- but what a pain to correct.