unexplained air leak

[iceman2009]

so today i screwed in my hpa tank ready to shoot some rounds in the back yard. since my house is quiet i heard an air leak turns out its coming from the top hole in the reg. i did not notice it this weekend when i went paint-balling cause it was loud and its a tiny leak. is there something i did wrong and how would i fix it. was it something i did wrong when i cleaned it? my marker is an 08 electra and fairly new