Toto Flushing Problem

I have a Toto toilet (purchased in 2001). It is a 1.6 gal flush with a G Max flushing system. It has worked fine untill recently.

Now when flushed it makes a strange hissing noise. It seems as if it is not getting the water it needs at the rate it needs because a vibration is set off in the plumbing pipes. Very annoying pounding noise - even shakes the small hoses to the water filter in the kitchen.

If anyone has any ideas as to what might be going on, and how to make the repairs I'd appreciate your insight.

Thanks Much

You need one of these...
http://korky.com/FillValveCapAssemblyR528.html

Or one of these...
http://korky.com/FillValve528T.html

A couple of the great things about a Toto toilet is that the repair parts are available in most hardware and plumbing stores, and they are not expensive.