weird vibrating noise

[ZEEM3R]

hey guys!
so few days ago i noticed a really weird noise coming from the car. it tends to happen when i start it but today i noticed it happening after driving it 20 miles home. it sounds like the sound the speaker systems make, like that static sound but when it becomes loud enough the car vibrates just a bit. it sounds like its coming from the passenger side sometimes but it also sounds like its coming from the rear of the car. I just had a new x pipe and test pipes put in and thought maybe they are loose but theres no smell of fuel coming from the car at all and i check my driveway every morning for any leaks and theres none so far. any idea what it could be?