  We study dissipation in Pd nano-mechanical resonators at low temperatures in
the linear response regime. Metallic resonators have shown characteristic
features of dissipation due to tunneling two level systems (TLS). This system
offers a unique tunability of the dissipation scenario by adsorbing hydrogen
($H_2$) which induces a compressive stress. The intrinsic stress is expected to
alter TLS behaviour. We find a sub-linear power law $\sim T^{0.4}$ in
dissipation. As seen in TLS dissipation scenarios we find a logarithmic
increase of frequency characteristic from the lowest temperatures till a
characteristic temperature $T_{co}$ is reached. In samples without $H_2$ the
$T_{co} \sim 1K$ whereas with $H_2$ it is clearly reduced to $\sim 700 mK$.
Based on standard TLS phenomena we attribute this to enhanced phonon-TLS
coupling in samples with compressive strain. We also find with $H_2$ there is a
saturation in low temperature dissipation which may possibly be due to
super-radiant interaction between TLS and phonons. We discuss the data in the
scope of TLS phenomena and similar data for other systems.
