The antonyms for the phrase "were quiet" are plentiful, as there are many words that describe the opposite of being silent. One could say that a group of people was loud, boisterous, raucous, or rowdy. Alternatively, one could describe the sound they were making as cacophonous, dissonant, or jarring. Some additional antonyms for "were quiet" might include tumultuous, clamorous, or vociferous. In short, if the goal is to describe an environment in which people are making a lot of noise, there are many different words to choose from, depending on the specific nuance that the writer or speaker is trying to convey.