We measured magnetic field noise induced in a copper disk, an aluminum disk and a brass disk for several conditions using superconducting quantum interference device gradiometer. The metallic samples were solid blocks, enamel-insulated dense coil-foils with several wire diameters, and a manually wound sparse coil winding. The metallic samples were positioned at 7 - 60 mm from the sensing coil of an axial first-order gradiometer with a baseline of 70 mm. Magnetic field noises were measured with the samples at room, liquid nitrogen and liquid helium temperatures. Intrinsic noises of the SQUID gradiometers were around 3 - 4 fT/Hz(1/2). Depending on the material type, the shape of the sample, the distance from the sensing coil and the temperature of metal, the magnetic flux noise was different, increasing to the range of 6 - 100 fT/Hz(1/2). We fabricated two-types of low-noise liquid-helium dewars with a different shapes of the metal plate for the thermal radiation shield for the multi-channel SQUID system for measuring the magnetocardiogram. We evaluated the fabricated dewars with comparing system noises and magnetocardiograms by using 64-channel SQUID gradiometer systems cooled in the fabricated dewars.