I noted this problem in various versions of miui, including the actual one. Mi phone is a Motorola Defy. To ensure it is not a config problem, I wipped all, then I installed lastest miui (stable 2.3.4a). For ensuring it is not SD card problem, I changed the SD card before starting miui. Then I start the phone. The sounds form ring, alarma and notifications are preselected to "silence". Ok... I choose some other ones. All OK but if I reboot the phone, the tones are again silence. The same problem happened in 1.7.15 and 1.7.8 and others. Any help please?