Wrost sound and even it could damage our ears
Is your phone ZB601KL or ZB630KL?
Please provide your firmware version: Settings > About phone > Build number.
For the sound quality problem, could you tell us does this appear on wired earphone/bluetooth headphones/phone's speaker? Does this appear with media/call/ring/alarm sound? If media, what app/app version are you using? Do you have a music link you can provide as an example? Could you describe in more details about the sound quality problem?