I first disabled WP-Minify which screwed up my CSS. So I did the usual switching permalinks to standard, then back to postname. Affter disabling W3 Total cache, the feed and podcast feed returned to normal. (There's disagreement among the W3 techs about caching feeds.) In the process, I also disabled a few other plugins (redirection, etc.) and disabled CloudFlare
Aftter re-enabling W3 Cache and restoring the browser cache lines in .htaccess, the feed structure remained o.k. So I restored CloudFlare CDN and unchecked "pretty URL's" in WP-Minify
Googling "feed" and "w3 total cache" brings up a whole slew of users who've had problems with Feedburner and W3. I didn't see any for standard WP feeds.