As fhnunez and said, it became some kind of a musical meme which is "a bit" overused in most trailers and action movies as well (if you watch the Cinema Sins channel on Youtube, you'll hear lots of 'em). And as YippieKaiYay said that's quite ironic since the most iconic "BRAAAAAAM's" are from the song "Mind Heist" by Zack Hemsey (the one from the trailer).
Edit. Here, a video is worth a thousand words
www.youtube.com/watch?v=830I9w7I7wM
"No no no no NO NO NO NO NO NO NO"
Ryan Stone, Gravity

I got the inception soundtrack and in one of the tracks there is an ending that sounds just like the sound that you describe. It comes right where the climax of that section should go so it is very noticeable. His music is very recognizable in other movies by the similarities with the Inception score and I have also heard variations of the BRAAM thing in those too. Could be that maybe?

I think it's referring to his Inception score, or perhaps the trailer music. If it's the latter, it's ironic because that wasn't even composed by Zimmer.