Launcher freezes for a few minutes before launching 13w38a and newer

Can't see any errors in the console- everything is exactly like normal until:
Client> OpenAL initialized.
Client>

Then it hangs for an extremely long time and both the Launcher and Minecraft window appear to be frozen; the close button won't do anything.
However once I get into the actual game everything works fine.
Once I click "Quit Game" on the main menu, both windows freeze.

If I kill the Minecraft process at any time, the launcher window un-freezes.

Selecting any older versions from the Launcher works perfectly (and takes 3 seconds to launch)... I don't even need to restart the launcher.