My AudioMoth lately has been producing a loud, high-freq. hiss on all my recordings. This happens no matter how I configure the unit. What causes this and what can remedy it? Thanks.

A few days ago I flashed my (then properly operating) AudioMoth with frimware 1.6. I had the batteries in. After flashing, I noticed the red LED on constant, and the green flashing. So, to set the time I ran the Configuration app and noticed that the time said XX. . . 1969. I did "Ctrl-T" and nothing changed. So, I attempted to flash it again, and I got the dreaded "No AudioMoth found." message/screen. Now my AM is dead. No lights, no response to apps. I've tried the paper clip procedure, to no avail; no response. Any suggested fixes? Thanks.