The noise you make when you refuse to listen to somebody and drown out their words with your own noise. Usually accompanied by sticking your fingers in your ears or shaking your head.
Found in plenty of music including songs by Jay-Z and BTNH, this would be used to represent weed.
Example: Roll, Roll, let's smoke, I got to get high
I been high since the last song, off that la la la lala la la
And I just been smokin' and smokin'
Smoke another blunt, roll another up -Bone Thugs and Harmony "Weed Song"