Yep, only two rubber mounts for the box. They mount on the side of the crossmember at approx a 45 degree angle and the bash plate bolts up to the crossmember at the bottom, no other mounts or rubbers. I've never removed the mounting spring as i've never had to take the engine out - gearboxes are a different story and to take them out i ususally remove the whole assembly, rear panel with mounting spring included - but i think the manual says what torque the spring should be.
Did the height adjustment cure the belt hitting? If it did and you still have rumbling try removing the bash plate entirely and take it for a test drive. I had rumbling in a niki once and that seemed to have cured it.
The only other thing i can think of is the mounting of the rear panel. I have seen different sized spacers between the panel and i have seen people assemble the rear panel with no spacers. The one with no spacers started making rumbling noises right on start up and was shut down straight away. I think the right amount of space is when the rear panel sits flush with the rear quarter leaving the bootlid sitting a little proud at the bottom (i think).
Those are things that i can think of that would make a rumble but as mentioned i've never taken the spring assy off so maybe check that thats all in good order before you start ripping bits off
