Have one toilet where the pipes in the wall occasionally start to clank once it is flushed. This sometimes stops fairly soon, other times continues for awhile. Flushing the toilet in the other bathroom, which is behind the first, usually puts an end to the clanking in the wall. Hubby first thought it was from the cold? But now it is quite warm and it continues.

Both toilets/tanks make a hissing or vibrating sound once flushed and take awhile to refill. Both are only about 3 years old. Any thoughts? :)

Most likely you need to change your fill valves. On most toilets the Fluidmaster 400 is a good replacement. I also recommend a new supply tube at the same time.

When installed, did u remove the cap on top of filler to clean out debris in water line. While open check washer for any defects.

Before removing cap shut off water supply. Remove cap, holding a bowl over filler turn water on and let flow for about 1 minute. Shut off water supply and reinstall cap. Turn supply on.

Let us know if this helps. If not may have to replace filler.

Chuck