Mastering.

Too much sub information for the speed of this song. Dig the tune and the bass has a good tone to it, just may be eating the fuck out of your headroom. I hear a fuck ton of clipping and pumping dude. Any higher than -8dB RMS fucks the punch in your drums up. What are you using for metering? If you're using something that averages the entire song together, the silent spaces will be averaged in and bring the RMS down. Use something that gives you constant levels like SPAN.