DIAGNOSIS This is typically audio clipping from an overloaded source, not a physically blown speaker. The internal amp is receiving a distorted signal.
FIX Check your audio source quality. In the Google Home app, go to the device's settings, tap Audio, and toggle "Disable audio normalization" or similar settings (the exact name varies). Test with a different music service (e.g., switch from Spotify to YouTube Music) to see if the issue is source-specific.
IF THAT DIDN'T WORK Lower the bass equalizer setting. In the Google Home app, go to the device settings > Audio > Equalizer. Reduce the Bass slider. The small driver can distort if bass is maxed out, especially on hard surfaces that amplify it.
HEADS UP If the crackling is present on all sources, at all volumes, and after adjusting EQ, it could be a failing speaker driver. This is a hardware defect, and if under warranty, contact Google Support for a replacement.