If the tensioner is new, the belt is new, and nothing is leaking such as coolant or oil and getting on the belt, chances are one of the belt-driven pullies is dragging when cold.
First, confirm there is no contamination on the belt. If there isn't, before starting the vehicle and when it gets bad, remove the belt and spin each of the belt-driven pullies. See if there is excessive resistance. Also, keep in mind that the alternator places the heaviest load on the belt when first started. So, as a test, when it's making noise, turn all electric accessories on to see if the sound gets worse. If it does, suspect the alternator may be failing.
One last thought. Is there any evidence of damage to the ribs on the belt? Is it running straight fully on each of the pullies?
Let me know.
Monday, November 22nd, 2021 AT 9:14 PM