Thanks everyone for the thoughts! Good ideas for me to check. The fresh-water usage is definitely something that I do only on big sails so checking the tank for the cause and inspecting the lines from it to the pump to the sink will be some of the first things I check.
Draining it out and seeing if it returns after the next sail might be a good thing.
Keep the ideas coming!
To answer your question, it's an encapsulated keel. No keel bolts for me!