RSS alert to email/ping me when keyword found in feed?

I'm having an unusually hard time finding an "RSS keyword alert" app, whether on the web or a desktop app.

Here's what I want to do:

- Enter an RSS feed.
- Enter my keywords.
- The app scans the feed at regular intervals, and alerts me (email? Growl?) when a keyword has been found.

I found some older web solutions that are now defunct, and have searched a variety of other usual places. Odd how this seems so hard to find as it seems to be a very common thing to do. I know on some sites like Google News, they have their own keyword alerts, but this is for specific RSS feeds not covered there, not the general news. For example: http://www.kvraudio.com/ssi/forum_43.rss

Does anyone use/recommend an RSS keyword alert app? Thanks so much.

Anyone have any ideas?

^ It's a clever idea, and I'm fond of Google's site: search too. But in my specific usage with the kvraudio forum listed above, it doesn't work as elegantly.

Followup for anyone who's been searching for the same thing: I found FeedRinse and paired that with RSS Menu. Still testing this combo, and I'm surprised there aren't more common solutions. FeedRinse tends to misfire on occasionally and report the WHOLE feed instead of just "rinsed" items, but isn't too shabby otherwise.