Whats the best way to remove old bondo?

[lukecp]

I was waxing my truck the other day, when i saw a little crack in the paint above the rear wheelwell. I picked at it with a key, and discovered about a 1'x2' patch of 1/4" deep bondo on my rear quarter panel, for no apparent reason. I can't seem to find any dent beneath it, but i haven't removed it all yet. I started with a sander, but it will take a long time like that, i am using 100 grit sandpaper. Is there any faster way to remove to old bondo, like a chemical or someting like that?