If no oscillation of the rod is obvious, when its position is moved, then the relevant damping is probably taking place within the 2.5 Ω solenoid coil.
It is possible ... likely ... that there is a super-imposed damping current in the coil that exists only when the rod is moved. The damping is due to the Joule Heating Effect, and is found in terms of I²R. You could devise some method of measuring the transient current in the coil, which would be separate from the 1 ma current that is a constant value.
There would be no other way for damping to occur. If the damping is is not mechanical, due to rod oscillation, the energy dissipation of the system has to be due to an independent current of some sort, as it passes through the solenoid coil resistance.