Water Heaters - Thumping in my water heater

A few months ago I started getting a loud thumping noise when I flushed any toilet in my house. Then I noticed it happening when the washer filled up too, but much louder. After doing some research I figured it was too much water pressure or water hammer(air or the lack of it.) But just now I figured out the noise isn't in the walls it is actually coming from the water heater! A little bit before all these problems started a plumber had to turn off my water to fix a leak and then he did something to the water heater to release some air. Could this be the problem causing the noises? And if so how would I fix It? There has to be a connection. Another plumber said I needed to put adapters on all my toilets and faucets but that sounds a little extreme. Any help would be great.Thanks