Voice / Sound bleeding over into another's parcel
To resolve this issue you will need to ensure that your description does not contain any unicode characters. These are characters that are non-standard and Linden Labs has confirmed that these are sometimes the cause of this issue happening.
1. Ensure that your land setting is checked to "Restrict Voice to this Parcel" under the Sound tab.
2. Remove the unicode from the description of the land.
3. Uncheck the "Restrict Voice to this Parcel" and then re-check the box.
This should now resolve your issue.