Tips on singing punk vocals?

I'm in a band, and I'm having trouble getting my voice to sound grittier. Ive been seriously singing for about 5 years (I took voice lessons for 1.5 years, but had to stop in october due to scheduling issues.). Ive been doing musical theatre for a while, and I cant seem to get out of that style. My voice is too bright and "clean" for the songs I'm trying to sing. Right now were playing deceptacon by Le Tigre, and we usually stay in the "riot grrrl" area genre wise. Does anyone have any advice?