On IFR arrival, Flight 4821 was cleared to intersection 17 NE of airport at 6000', then for ILS runway 23 approach. Radar service was terminated 6.5 east of intersection. Radar data showed that flight crossed and then bracketed localizer. Flight intercepted glide slope from below about 7 miles outside of outer marker and thence deviated above glide slope. About 2 miles outside of marker, flight was at a full fly down deflection when it entered a descent varying from 1200 to 2000 feet per minute. Aircraft struck wooded mountain top 2.0 miles inside of outer marker (3.9 miles from runway) at elevation of 2280'. Minimum altitude at marker was 3600'. Glide slope elevation at point of impact was approximately 2900'. Evidence was found of inadequate electrical ground path between radome and fuselage which, when combined with existing weather conditions, may have produced electrostatic discharge (precipitation static). Although post-accident tests were not conclusive, the Safety Board believes that the glide slope indications might have been unreliable due to precipitation static interference.