['LIVEWIRE?']

Having been through this radio with the proverbial toothcomb, I am at a loss to know what has happened. There's nos sign of internal damage- i.e. no loose or missing tuning cores from I.F. and other cans, no cracked or dislodged components, the tuning cores can be moved through the RF & Osc. coils from LF to HF by rotating the control as per usual, all the valves are OK, and all DC voltages are normal, but no signals are being received, just an almost constant crackling along with the usual FM 'hiss', the cause of which I cannot pin down. The radio appears to be oscillating, since, with the cover off the FM Tuner box I can detect it on another FM Radio. Can anyone shed any light on this, please?
At the moment I am without a working FM sig. gen.(haven't had time to repair mine!) which compounds the problem.