No Audio, Samsung Galaxy S4 (Sprint)

A few weeks ago, my phone's APN list got corrupted, causing me to lose mobile data; a series of firmware flashes, modem updates, and backups and restores eventually fixed the APN problem, but now the entire sound subsystem is non-functional. The speaker and microphone do not work in any app, and give errors that cause me to believe it's a software problem.

Example symptoms:

• Dialer - pops up a "stopped responding" dialog when making or receiving calls; selecting 'wait' in the dialog allows the call to complete, but with no incoming or outgoing sound.


• Sound Recorder - pressing record pops up a dialog "Internal Application Error. Microphone may be in use."


• YouTube - all videos show "There was a problem while playing. Touch to retry."

Phone details:
Samsung Galaxy S4 (Sprint), model number SPH-L720. Rooted, running Android 5.1 (& 4.4) (CyanogenMod-12.1 various nightlies (see below) and CM-11 snapshot).

Things I have tried (without success):

• Factory Reset (without restoring backups, just to see if sound works)


• Re-flash various ROM versions; cm-12.1-20150917-NIGHTLY, 20150922, 20150926, 20150928, and cm-11-20141112-SNAPSHOT-M12-jflte. The 20150917 nightly and 20141112 snapshot versions have previously had sound working, so it's not a bug in new ROM versions.


• Combinations of the re-flash with factory reset.


• Reboot with SIM card and micro SD card removed.


• Re-flash modem/baseband to earlier version (was running OH1, now running NAE; have not flashed all the way back to MF9, which is the version that was running the last time I'm sure sound worked, but this was a move of desperation, since the modem firmware shouldn't impact the sound system.

I'm at my wits end. I feel like with the above, I've re-initialized every location that could possibly be affecting the sound system, and yet, I can never get any audio input or output from the phone. Please help.