I think the same sound may be produced by something in the workshop when a peep is working on career out there. I've heard it a few times when I was nowhere near the shredder - it caused me to check to make sure nobody was goofing off by shredding documents.

There's also the sound the washing machine makes. That's caused me to wonder what's going on a few times.

Yep, it's the shredder. I clicked on it several times and heard the sound that I had been questioning.