Repairs L100 making bad music

My aged L100 makes a fairly bad grinding noise when I release the clutch/brake. It still runs well but doesn't sound that sweet Deere noise. As best as I can tell it's coming from under the seat. I moved the drive pulley but it feels solid. How can I diagnosis this problem (I'm terminology deprived).

I read a similar earlier post, replaced the two idler pulleys and 30 minutes and $14 later she works like a charm.