RSS feed doesn't validate

A few days ago I started getting an error message from Feedburner

It says

Sorry

This feed does not validate.

line 729, column 0: XML parsing error: <unknown>:730:54: junk after document element [help]

</rss>

What doesn’t validate is a long string of nonsense inside script tags. It’s about 50 lines long and includes things like $=~[];$={___:++$,$$$$:(![]+"")

I’ve tried deactivating all my plugins, changing to the twentyten theme, I’ve checked my last few posts for wonky characters. . .

I’m NOT a programmer and don’t know what to do. I really, really don’t want to have to uninstall my blog and start over as it’s been running for two years now and I have almost 250 posts. Yes, I’ve got backups, but still. . .

Please help.