http://kotaku.com/5483162/portal-mysteriously-updated-with-secret-radio-codes-new-achievement

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Valve's brilliant first-person puzzler Portal has just been updated. Not normally a big deal, but when that update adds a new, mysterious Steam achievement and some hidden radio transmissions and this is Valve we're dealing with, we're right to be curious.

Today's Portal update, officially, features the following addition: "Changed radio transmission frequency to comply with federal and state spectrum management regulations." Not officially noted there is the new Steam achievement "Transmission Received" which goes undescribed by the developer, but involves the use of Portal's in-game radios.

Also included, as spotted by Steam forumgoers are a bunch of new sound files, all prefaced with the word "dinosaur." According to members there, those sound files feature Morse code encoded transmissions.

While we have no idea at this point what Valve is planning—the Steam mob is currently pounding away at a solution and Morse code experts are encouraged to join the fray—we wouldn't be surprised if the Half-Life and Left 4 Dead developer was planning a Portal related announcement. If it were to announce Portal 2, we wouldn't be surprised. If it were to announce a sequel to one of its games in its own game, we'd simply be impressed.

Given the close relationship between Portal and Half-Life, we could also be looking at a separate game announcement, like the long-awaited Half-Life 2: Episode 3. Whatever the case, we're excited and keeping a close eye on updates.

Update: New sound files, including this new computerized voiceover from something that is not GlaDOS and these transmissions, have been making their way to YouTube from users. Give 'em a listen.

The game continues, with those sound files containing data for equally mysterious images. There's plenty of code-cracking to be done, as Valve is going hog wild with this multi-layered puzzle.

Changed radio transmission frequency to comply with federal and state spectrum manage [Steam Forums - thanks, Alex!]"

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Interesting stuff, I'm hoping this leads to something new for Portal and hopefully leads to something about Half-Life 2: Episode 3. The processed images look strange, lol.

Will you try and figure out the puzzle?

I'm following the thread and it's pretty interesting. Apparently it's up to the point where people have discovered a BBS number and are trying to connect to it to get the next clue.

There has been a slight addition to the ending of Portal.

*edit*

I just played through it today and after you defeat Glados, you hear footsteps of a robot/android who thanks you for assuming the party escort position and starts to drag you away.