Toto Drake leak from tank, not flap valve

I have a 2-yr old Toto Drake that I had installed. A few months ago it started to make a chugging sound and I verified that water was leaking into the bowl from the tank. I contacted Toto and they sent me a new flap valve because I was having problems locating one locally.

That seemed to work at first but within a few days the sound came back. It's not consistant, just start up maybe three-four times a day.

Other than the flap valve, what could be causing this?

There is a gasket on the flapper valve seat. It could be loose and water is seeping out through there. If that is the case, you'll have to remove the tank, tighten the (big) nut holding the flapper valve seat, then reassemble. Make sure there is enough slack in the chain, it should not have much, but needs enough so gravity and water pressure lets the flapper seal - it can't be held up slightly by the chain being too tight. Lowes usually has the flapper valves for Totos in stock and a plumbing supply house probably does as well. They are made by Korky. Make sure there isn't something caught or built-up on the flapper valve seat...rub your finger around it to make sure it is smooth.

Thanks, I just gave your suggestions a try. Let's see if it works.