I have a larger alternator on my car, which stresses the belt tensioner more at idle.

Installing a clutched alternator pulley will make the drive belt last longer, the shock last longer, the spring last longer (mine got a stress crack!), the tensioner bearing last longer; and it will put less stress into the timing cover and crank pulley. There's a reason they became universal on diesel cars once they were introduced in ~1997.

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The problem is caused by the alternator pully clutch being seized or having been replaced with a solid pully. this will only show at engine idle, the noise coincides with excessive vibration of the belt tensioner and overheats the shock cylinder. Reconditioned alternators usually come with a solid pully and is easily overlooked.