Now I know 7 type cars arnt exactly rolls royces but the engineering side of my brain tells me something is going to get damaged if this continues.

Car: Haynes roadster, Ford I4 2l engine, on rubber engine mounts.

At around 3000rpm there is quite a harsh resonance sounding vibration. Above and below this the engine sound/feel is smooth and hollow sounding, but between 2800/3200 rpm is sounds like the crank is connected directly to the chassis!

Has anyone experienced anything similar to this?

Is it whilst you are stationary or moving?

Either, while free revving or under load

This is common where you have a vvt engine, if you fit a fast road cam that makes it worse.

http://sylvabuild.blogspot.co.uk/2013/07/road-trials.html