Per Robert S. request I visited the plenum at each station (Corner, Mids and Ends) to check for the HVAC grating installed sometime in 2009, it turns out that only the Y-End station and Corner station have such device installed, see photos.

Something to note, while visiting the Y-End station plenum the fan started to pulsate with the door open, I did not see such response on the other stations, but with the door closed the pulsation goes away.