The analysis of the Kepler light curves of red-giant stars revealed a few hundred stars with low-amplitude dipole modes. Various mechanisms that could damp the modes have been proposed including a magnetic field in the core, a peculiar internal structure, or binarity. However, none of these hypotheses have been confirmed. To gain insight into the damping mechanism we investigate the peak properties (linewidths and amplitudes) of the radial oscillation modes. Since it remains unclear if and how these modes are affected, they can provide additional constraints on the damping mechanism. We compared the radial mode properties of suppressed dipole mode red giants with the proper- ties of a control sample. We present the results of this comparison and its consequences for the proposed hypotheses.