Is this phenomenon capacitive coupling or human antenna effect?
You don't have a very well-shielded coax, or the coax is poorly terminated, or the wiring to the shield-braid is broken or long and thus has lots of inductance.

These conditions are making the SHIELD be hot. At 90MHz, wavelength is 3.3 meters, and quarterwave is 0.8 meters or 32 inches. Quarterwave antennas can serve as impedance transformers between infinity and Zero, thus generating very high voltages at one end and very high currents at the other end.

Summary: your cable, connectors, pigtails, braids and terminations are suspect.