replacing the brake rotors

I just replaced my brake rotors with brand new Brembo rotors. I also put brand new pads and sensors. I took it for a ride, when I heard a taca-taca-taca noise coming from the rear. I took the wheels off, I cleanded everything. Nothing.
I took it out again. It does not make the noise when you step on the brake, but it does make the noise every once in a while. The noise only lasts for 4 seconds tops.
Any ideas?