Question: On my Xubuntu 13.04 installation, when the sound is turned up to high levels (>50%), it begins to (randomly?) fluctuate between loud and quiet. In pavucontrol, the port setting is fluctuating between "Analogue output" and "Headphones" (I'm using desktop speakers plugged into the integrated audio line out).

Any ideas?

Answer: 
There *is* a simple binding for "Select all" in gtk: `C-/`

It’s defined as a general [GtkTextView signal](https://developer.gnome.org/gtk3/3.4/GtkTextView.html#GtkTextView-select-all) and not specifically part of the emacs key theme. But it works fine with it. It's defined as an alternative to `C-a`. While the latter gets reinterpreted by the emacs theme `C-/` remains valid for "Select all".
<http://www.emacswiki.org/emacs/EmacsNewbieKeyReference#toc8> appears to be what you're looking for ( C-x h after setting marker )

Also, depends on whether you want the 'page', or buffer, etc.