Apple Watch Series 9 speaker or microphone is muffled

The checks in more detail

A call where you are faint may be improved by holding the watch near your mouth, since the microphone sits on the case. If the speaker crackles at all volumes after cleaning, Apple should check it. A Series 9 that has been dropped can have a damaged speaker membrane. Apple's guidance for sound problems also suggests restarting the watch, then the iPhone, and checking that the watch is not in Theatre Mode, which silences the speaker and keeps the screen dark; a swipe of the Control Center icon shows it.

If calls ring on the iPhone but not on the watch, check Settings, Phone on the iPhone for Calls on Apple Watch, and ensure the watch is unlocked and on your wrist. In a very noisy room, hold the watch near your mouth and speak clearly; the microphone works best at a short distance. If the Series 9 has been exposed to hot water or steam, let it dry before using the speaker. If sound plays only from the iPhone while a call is on and the watch seems silent, check the Handoff-style setting that routes calls:

in Settings, Phone on the iPhone, Calls on Other Devices, and in the Watch app, Phone, Answer on Watch or Answer on iPhone. A call that answers on the iPhone leaves the watch quiet by design. Choose the answer behavior that matches how you use the watch. Make sure the watch's software is current, since Apple fixes audio issues in watchOS updates, and, if the problem began after an update, check Settings, Sounds and Haptics for changed settings. A watch that is silent only for alarms should be checked in the Alarms app, where each alarm has its own sound and a volume that follows the watch's alert volume.