I just got my 914 back on the road today after a complete makeover. Among the items we upgraded was the alternator. Now that the car is running it developed a screeching sound after 120 test miles. I’m attaching a video clip where we were able to reproduce the noise by pulling on the fan belt. The alternator and tin are tight and not wiggling.

Any thoughts?

Click to view attachment

All belts stretch after first set-up and require a retighten,check the following;
is the belt the right size ?,
is the pulley in good condition,
is the altenator fully lined up with the cooling fan drive,
are the mounting brackets in the right spot,these mounting is adjustable ,are they straight and not cracked.
Good luck.