Exclamation [Q] HTC One hearing nothing but static

Hello. I've Googled and it seems that getting a good amount of static is a noted issue among HTC One users, but my issue is I hear nothing at all but static. Really loud, painful static. The problem only occurs during calls without the speaker on and any time I use my headphones. If I put the caller on speaker or just blast my music, everything is fine. And the static doesn't end immediately after I end the call/music

I've been using this phone for about a year now, and the problem only started a few weeks ago. I've tried using both my Sony earbuds and the Beats earbuds that come with the phone. I sent my phone for servicing last week, highlighting this problem. They kept it for four days and then said the failure was a "program abnormal execution/termination (Error massage[sic?] pop-up or etc...)" and "re-flashed ROM image" as a solution. I made one call to my sister after that, and lo and behold, we could hear each other, but there was still static. And then there was a sound my sister describes as a rocket rushing past and I had crystal clear sound like the good old days after that. Likewise with listening to music/videos. But today the static came back. It wasn't the same loud painful static as before, but it's still nothing but static. I've tried turning off Beats Audio and rebooting the phone but the problem is still there. As I've just transferred my data back into the phone, could it be possible that I've reintroduced a corrupted file that triggers the problem?

I'm on Andriod 4.4.2 and HTC Sense 6.0. The phone says there is no upgrade available. I live in Asia, so this does not seem to be a Three network problem as well. Any help on this will be much appreciated. I really dread having to send my phone for servicing again.

Thank you!
[x-posted to HTC forums, but hitting a wall there]