11:33 AM PT -- 5/7 -- TMZ Sports has obtained the police report in Ross' arrest ... and it turns out, the Cowboys' D-lineman was initially pulled over because he was playing his music too loud.
According to the officer, he "could hear and feel loud music" coming out of Ross' silver Dodge Charger ... and says Ross revved his engine loudly as well.
The cop states in the report that because of the noise and the fact that Ross had temporary plates on his car, he pulled the guy over.