Odd sound 2000 s80 t6

[IndianaS80]

Hi all! New around here - thanks for having me.

I have a 2000 Volvo s80 (87k miles) that very intermittently makes an odd sound. Timing belt was done at 50k. Had my mechanic check the serp belt, tensioners, and pulleys. Unfortunately, the sound never reproduces when it’s in the shop. Any ideas what might be causing this? Seems to be coming from the passenger side. Here’s a short video: