repacked system image fails to boot

I have a problem where the repacked system.img does not work. My target device is: DOOGEE X5pro, which uses MT6735M chip. I am using this custom ROM. The original files from this custom ROM works fine with the device. I wanted to change something in the system.img and the following is what I did. $ simg2img system.img system.raw $ mkdir tempsys $ sudo mount -t ext4 -o loop system.raw tempsys $ cd tempsys Here I made one change. I didn't like the camera shutter sound so I simply deleted the 'camer_shutter.ogg' file in tempsys/media/audio/ui. $ cd .. $ tune2fs -l system.raw here I check that "Block count : 390111", "Block size: 4096". I multiplied these two values and got "1,597,894,656". $ sudo make_ext4 -a system -l 1597894656 -s sys3.img tempsys BTW the permission of the sys3.img is as below: $ ls -l -rw-r--r-- 1 chadrick chadrick 1327287648 2월 18 16:09 sys3.img I'm not sure if the permission of the system.img file matters before flashing it to the phone. I shall proceed just as it is. After flashing it, it is stuck at the boot logo. I guess while the device succeeded upto loading the 'boot.img' but it failed to properly deal with 'system.img'. Apparently, could someone point out some things that I may have missed? BTW, I did the same repack operation WITHOUT modifying any contents in with system.raw file. The repacked system.img still didn't work.