Okay, same issue, but I am FIRMLY convinced this is software, not hardware.
I installed "Alarm Clock Xtreme" from the Amazon "app of the day" page. I set a test alarm to try it out (while listening to a podcast through headphones) with the option to "escalate the alarm" volume. The alarm screen showed up, but I never heard an alarm (speaker OR headphones) and since then the only sounds I get from my speaker is a static-electrical POP sound when I remove my headphone plug or when my PE wakes up or goes to sleep.
I'm angry that the app in question seems to have mucked around with some root-level sound option that I don't know where to go to access.
Running 2.2, rooted with z4Root. Have tried uninstalling and reinstalling the #$%#$ alarm clock app, as well as wasting a few hours trying to set up the sipdroid/pbxes/googlevoice/etc. thing, all to no avail. (I've lost track of how many new accounts/phone numbers/pbx boxes/mail-order-wives I have set up now.)
Any thoughts on things I could check out with the terminal emulator or othersuch tool?