zetec2,
centre line closure was also a feature of the same engine in the Javelin. A trick of the engine fitters at Middleton St George (33 Sqn) was to ground run the engines just when the film was starting in the cinema. The tin roof used to resonate in tune with the rumble and render the film almost inaudible.
If my understanding is correct the J35 may suffer something similar and the solution may be akin to the old method.