Has anyone heard this engine noise before?

[Richard B]

A few days ago I noticed a new noise. A rythmic / phasal squeal most likely emerging from one of the pulleys on the serpentine belt.

At idle, it phases from low to high volume at 15 to 20 seconds intervals. At higher RPM the phasing is faster however the pitch of the squeal doesn't rise.

You can hear it start 16 seconds into this video, and stop at about 19 seconds. (it's actually audible the entire time, just peaks at 16 to19s, and much louder IRL)

Direct Link to video (sorry my attempt to embed didn't work)

What do you think is most likely the source of this?

 

[Richard B]

Solved it. All it was was dust on the inside of the belt. The car had been near a minor dust storm whipped up by a leaf blower. The underside tray is missing on my car so dust blew up into the engine bay from underneath. I'm not a great fan of lubing the inside contact area of a multi-V belt, but it worked.