My first guess is that you have a dragging caliper or maybe the heat/water shield is loose. I'd take the front wheels off and have a look. Nothing should be loose around the brakes, hub area.
Not that unusual for many engines to vibrate more at a certain rpm, a modified intake can sometimes make it more noticeable. Also could be that it's an issue with the exhaust, either that it's touching under the car and transmitting that vibration to the cabin, or maybe it's just dented somewhere and causing more vibration under hard acceleration.