Note2: A 4.3 bootloader looks like this (i9505 is same as our phone):
KNOX kernel lock and KNOX warranty void are the new things in the 4.3 bootloader that can break warranty easily via CF-Auto-Root.
So just now I remembered something from here: http://forum.xda-developers.com/show....php?t=2253528
To sum up, it says that the LTE Modem from 4.3 (MK2) would break sound. So to avoid that, just use the LTE modem from MDL and the GSM modem from MK2. I tried it and it works!
1. Download this zip: https://www.mediafire.com/?7tj2smth2vp1b7m
2. Extract the files inside the zip into anywhere you want, as long you remember where it is.
3. Put your phone into download mode (vol down+home)
4. Open odin, click on phone, select Modem_UVUAMDL.tar, untick auto-reboot, and press start.
5. When the install finishes, manually reboot it back to download mode.
6. Using odin again, click on phone, select modem.bin, untick auto-reboot, and press start.
7. When finished, reboot and you're done!
If you already have the MDL modem installed, just ignore steps 4 and 5.
To revert to MDL, skip steps 5-7 and only flash Modem_UVUAMDL.tar.
Credits to: @j_r0dd for the 4.3 modem, @mrvirginia for the 4.2.2 modem, and the devs over at the i9505 section for figuring out the trick