Call audio drops sporadically

I'm using SoundAbout v2.5.3 on an HTC Evo Shift (android 2.3.4). Like many other Evo Shift users, my ear speaker suddenly stopped working (for call audio) a while back. I've read posts in other forums that suggested the ear speaker should be replaced as the slide cable is likely at fault. However, I wasn't convinced that was the problem since the ear speaker would actually work when the keyboard was slid out and for other non-call features.

After much testing, I've found that I can get my ear speaker to work temporarily if I use SoundAbout to route media sound to the ear speaker and then play something through the media player. For some reason this restores my call audio to the ear speaker. (Simply using the SoundAbout setting to route Phone call audio to the ear speaker didn't work.) However, there is something (i.e. another app, process, etc.) that "kills" the ear speaker sporadically and I can't figure out what it is. I've completely wiped the phone, restoring it to its factory default settings and that didn't help. I've disabled the Wired Headset detection in SoundAbout and that didn't help. I'm running out of ideas/options. I really appreciate that SoundAbout works to restore my ear speaker...just wish I could get it to "stick" so call audio doesn't drop. Any ideas how I can further diagnose or fix this issue?