Mine has the exact same vibration you describe- @1.5k rpm. I thinks it's just a harmonic, like a range the engine doesn't like, once you're past it goes away.
2011.5 LeMans Blue e92 DCT, ZCP, European Delivery. Edition Grilles, Reflector delete, Rear Fogs Enabled, Borla/Encore Innovation Exhaust, LUX Angel Eyes, 255x285's, Dinan 3.45 Rear, BPM Stage II. "Last of the V-8 Interceptors, a real piece of history..."