General Antonyms:
* Quiet
* Silent
* Still
* Peaceful
* Tranquil
* Serene
* Hushed
* Soundless
* Mute
* Calming
Antonyms Related to Specific Contexts:
* Subdued (for sounds)
* Soft (for sounds)
* Muffled (for sounds)
* Unremarkable (for crowds or events)
* Peaceful (for environments)
* Solitary (for environments)
* Calm (for people or behavior)
* Relaxed (for people or behavior)
* Composed (for people or behavior)
The best antonym to use will depend on the specific context in which you are using the word "noisy."