Guys I bought one few weeks ago and I just noticed oppoF1s has a sound issue, when battery is less than 40% the ringtones sounds will be coming directly at the back of the phone not fron tje bottom where the speaker is located and the sound is like a internal crackling sounds but it only applies pre installed ringtones not on music. Anyone can help me teoubleshoot this because if theres really a problem with the component the issue should also occur on both music and ringtones right? Is it normal? And after I restarted the phone it came back to normal but after a minute it goes desame and the issue isnt occuring alreadu until I charged the phone. So I suggest you not to buy it at this cost. . .