I have not yet seen or heard any remarks about Palin's backyard presser that mentioned her vocal and breathing qualities.  I heard her sucking in air and saliva at intervals (much like an asthmatic), staccato speech, and a reliance on her stock phrases, but in confused cadence.  It all indicated high-anxiety and extreme urgency, as though it were necessary to announce her resignation before Something Else were announced.  Yes, being the announced target of an investigation could cause it.

Ms. Point Guard got in her licks at the Mean Media, poked a stick at Mark Sanford's foreign trips, bogusly called herself a lame-duck, declared "We can do more good ooutside of government," no politics-as-usual, the need to raise her family, blah blah.  None of it makes a lick of sense.  Those "reasons" would not cause such panic.  Watch the presser again and listen TO HER VOICE AND BREATH; it is so evident that something is about to break.  It's almost like you can hear the sirens coming toward her.

Also: please take note of Lake Lucille in the background, and listen for the laughing Lame Ducks and Loons...