I have change the sound file in the apk-file and it dosn't work as well. I check the Log and the source. In the line 136 (I mark it in the folowing link) the exception catch any problems. I test it and the sound of the exception (DeskClock.apk: res\raw\fallbackring.ogg; higher sound) is differend from the original (Timer_Expire.ogg: deeper sound).
I get in the adb Log some errors:
ACDB-LOADER: Error: ACDB AudProc vol returned = -8
ACDB-LOADER: Error: ACDB AFE returned = -8
AwesomePlayer: LPAPlayer::Clip duration setting of less than 30sec not supported, defaulting to 60sec
AlarmClock: Using the fallback ringtone <<< This is the excpetion!!!
Some of the errors are identical in the original and modified version. I create a ogg-file with the quality 5 and metadata with the title: Time_Expire and ANDROID_LOOP: true. All that don't work and use the exception sound. I change the fallbackring.ogg as well and no sound is playing. After changing the fallbackring.ogg a file not found exception is called.
Maybe it is a signing problem. I check with the folowing command the signing of the modified apk and get the error: jarsigner: java.lang.SecurityException: SHA1 digest error for assets/sounds/Timer_Expire.ogg
jarsigner -verify -certs -verbose "DeskClock.apk"
Now I think the Timer_Expire.ogg will not be loaded and so the exception is called. The tool Easy Apk Dissassembler can dissassembly, assembly and sign an exisiting app. The problem will be that we don't have the sigining key from google. I don't know what happen if I sign it with my own key.