Apple Watch Series 8 speaker or microphone is muffled

The checks in more detail

and a call where you are faint may be due to the iPhone's relay or a poor connection. Siri that does not hear you may need the Hey Siri setting, since the watch listens only when raised or when you say the phrase. If the speaker crackles at all volumes after cleaning, Apple should check it. A Series 8 that has been through hard impacts can have a damaged speaker. Remember that the Series 8's speaker plays the loud Crash Detection and Fall Detection alert tones and the emergency siren feature used by the Series 8 for Emergency SOS, so a test of the speaker at full volume should be brief.

Check Settings, Sounds and Haptics for the alert volume slider, and run the Ping iPhone and Ping Watch tools from Control Center to test the speaker without a call. If the watch rings at a low volume only, drag the slider up in Sounds and Haptics; the setting is separate from the media volume. If your voice is faint on calls but sound from the watch is fine, the microphone opening on the side of the case may be blocked by a bumper case or a band; remove the case and look at the left side of the watch.

Cleaning with a dry, soft brush removes lint, and a barely damp cloth removes sunscreen. Avoid sprays and solvents. If cleaning does not help, record a Voice Memo on the watch to see whether the problem is the microphone or the call. Because the Series 8 can place calls on its own on cellular models, check whether your voice works on a call made through the watch's cellular and on one made through the iPhone, and compare, since a fault that occurs only on one path points at the watch's microphone or the iPhone's relay. Note the result for Apple Support, which can then focus on the right part.