Underground cables and resonances in range of frequencies
I general ALL power-lines exhibit resonances that vary with timeframes that are both long and short.

To see why all you have to do is realize that the power-line is subjected to many different loads, some of which are Inductive (motors), Capacitance (Fluorescent lights), resistive (heaters) to list just a few.  Longer tem variations arise from people turning on loads, say a washing machine or lights and indeed even a change in the mechanical load seen by a motor will change what electrical load it presents to the power-lines.  On shorter time frames, there is variation even on e a cycle to cycle basis as the sinusoidal waveform interacts with rectifiers, chopper circuits and switching power supplies.

You can see where a C load in parallel with a L load might form an easy resonance.  This resonance might exist for long time frames, or the power-line may only see the C art of the resonance during part of the sinusoidal cycle.  These L'and R' and C's are also distributed spatially thorough out a neighbourhood, so this ends up to be a seething complex time varying mess.

Buried cables, due primarily to the fact that the line and neutral wires are closer together tend to have higher capacitances than an air/pole mounted power-lines.  That means that the resonances can be enhanced, depending upon the primary inductance that are present.  Although it must be mentioned that it is possible that a buried cable can have fewer resonances also because of the increased capacitance.  It all depends upon the mix of equipment and parasitic impedances.