"Going on a rampage" means to get really angry, make a lot of noise, and cause problems. A good way to imagine a "rampage" is to think of a wild animal that gets loose from the zoo. Or, if you've ever seen a "Godzilla" movie, you can imagine one of the giant monsters destroying a city.

The other situation that people use "rampage" for is when someone goes crazy and kills or hurts a lot of people. This is a sentence from a newspaper report:

Police say that Jones, age 42, went on a shooting rampage at a local shopping mall, injuring 12.

To "go on" a rampage means to start acting that way:

Chuck goes on a rampage when he sees people sitting around and not working.

While it's happening, you say that someone is on a rampage.

Watch out. Chuck's on a rampage.