Vibration from Passenger Floor Board

I have a '12 Malibu 2.4 with 42k on it with a pretty good vibration in the gas pedal and passenger floor board but not the steering wheel. I just had new tires put on since it was time but the vibration was there before and after the new tires were put on. Wheel bearings seem tight also. I had the motor mounts checked when it was at the dealer and no issues there. Could it be a drive axle? You can feel it at low speed but gets worse as you drive faster.