I doubt that parts are breaking free from the airplane and floating to the surface. Within the general search zone, the minimum depth is 864 meters, the maximum depth is 4606 meters.
Pressure increases in the ocean at roughly one atmosphere for every ten meters of depth. What made a section of the plane buoyant at the surface would likely be crushed at the depths this plane is now lying at. I doubt that honeycomb structures are designed to withstand hundreds of bars of pressure.