[Q] Both speakers died suddenly topic

Yesterday I was listening to a podcast through my M7's speakers and the audio cut off suddenly - as if I had tapped "Pause". Since then I have been unable to get any audio out of the phone speakers. Bluetooth audio seems fine. At first I thought that headset-jack audio was gone, but now it is just very low volume (maybe it was low all along, or maybe it was gone at first and is now working but quiet after a few Nandroid restores).

Here are the things I have tried:

Calling the phone to get ringtone
- (vibrates but no ring)
Restarting
- (no change)
Restoring Nandroid backups from 2 weeks and 2 months ago, with same ROM
- (no change)

Restoring Nandroid from over a year ago, before I had installed any custom ROM:
-Touchscreen doesn't work so can't use the phone (?!?)
-Speakers still seem broken - receiving call causes vibrate but no ringtone
-Had to ADB into the phone to reboot to recovery

Current ROM: CRDroid/CM11

I can't even guess at what would have caused this - I was doing nothing unusual or stressful with the phone. It was sitting on a table playing the podcast & the sound just stopped - pretty sure there was no "Pop" or other sound. As far as I know both speakers were working fine before yesterday, but since I mostly listen to spoken word I guess it's possible that I haven't noticed one of them being out.

Oh yeah, I found and tried dialing the phone diagnostic code (something like *#*#3424*#*#) but it did not work - I'm guessing it just isn't supported in the CrDroid ROM.

Any advice would be much appreciated. Is there anything I can do to test or determine whether this is a software or hardware problem? It seems bizarre that both speakers would just stop working, but what do I know?

thanks in advance for any assistance...