Who performed Grover in CinderElmo?

I was watching CinderElmo a few minutes ago, and it seems that Grover was preformed by somebody else and Frank dubbed the voice in. There's a part where Grover says, "Yes, sir!" and it doesn't sound like him. So who do you think preformed Grover in CinderElmo?

So, does anyone have any ideas?

Maybe Frank and Eric alternated? I've noticed from time to time a sudden switch in Big Bird's voice between Caroll and Matt.

The "Yes, sir!" line didn't sound like Eric.

I listened to it several times, and it sounds like Kevin. But, I don't think it could have been him. If only I had a way to post the clip on YouTube, so people could correct me.

I had a thought... maybe it was Rick Lyon... I remember from his website years ago (maybe still there, I don't know) him talking about working on CinderElmo, and there was a picture of him posing with Grover in his wardrobe, and explaining how he felt Grover was the world's most perfect puppet because of his construction and flexiblity.

http://www.lyonpuppets.com/grover.html

"I got to puppeteer Grover in several scenes in the palace -- no key scenes, of course, just background stuff and one large group dance scene."

Well, it looks like Grover had multiple puppeteers in this one.

I asked Rick about it, and here's what he said: "There were actually several people in Grover throughout the shoot. But mostly Kevin Clash and Steve Whitmire, as I recall, and me just in crowd scenes like the ball. This was long before Eric Jacobson started doing him." So that clears things up.