First, check if the sound quality issues occur when you are connected via 1) Bluetooth only, 2) AUX only, or 3) both Bluetooth and AUX connections.
If 1), the problem could be due to your phone being too far away from the Soundlink, so try moving closer to it. If this doesn't resolve it, your phone may be overworked, so try closing out of any excess apps and turning off Wi-Fi.
If 2), the issue could be with either the AUX cable itself, or the AUX port on either your phone or the Soundlink. Try using a different AUX cable to test this. If the problem persists despite using different cables, it may be a problem with the ports.
If 3), there may be something faulty with the Soundlink's speaker itself. This would require replacement of the speaker.
For further information, please visit our [[Bose Soundlink III Troubleshooting#Section_Speaker_sounds_distorted_muffled|troubleshooting page]].