when i connect the phone to an external speaker and press play in the music app i can hear a weird sound like a "plop" just before the music starts and then the volume goes down to almost 0, but when i connect the headset (headphones and mic) everything its fine and no "plop" sound so i realize that must be a software problem.
Also if you connect the aux cable just the half of the connector it detects the cable as a headset then insert the connector all the way down and everything plays just fine with no "plop" sound before the music starts but is annoying to do that all the time so heres the solution.
This may work in other zte or chinese phones.
1.- Go to enginer mode: to do that dial *#*#3646633#*#* then go to hardware testing, select audio, select Headset Mode
In type go to media and Set the Max Vol. 0~160 to 104 and set
thats all !!!
Tell me if it works for you