Has there been any change in flavor/aroma? You said that the excessive foaming is "recent", which I take to mean that you've been doing this a while and the beers never foamed up like this before.
If you can taste/smell phenolic flavors/aromas (clove, band-aids, adhesive or electrical tape, smoke), that shouldn't be there, then you might be suffering from a wild yeast infection. Star-san is ineffective at killing wild yeasts. You can try to use a different sanitizer such as iodophor, or even bleach (after which you could THEN rinse fully and re-sanitize with star-san).
If that is the case, it also would be a good idea to replace your plastic and rubber components that touch your beer on the cold side.
HTH-