Strange vibration type noise?

[TVR Beaver]

I have a strange noise, only when the engine is very hot, only when going up the rev's at 1500 and again at 2100 rpm and only whilst driving?
It is getting worst as time goes by but still not doing it standing still so it’s a bugger to find. I've changed the power steering pump, run the engine with the belt off, looked at my Ali trumpets in the plenum etc, etc. on the odd occasion it has done it whilst revving the engine at standstill but as soon as you open the bonnet, nothing? Although initially it sounded like something rotating I'm starting to think it may not be... and have my suspicions about the large dustbin cat.
Does anyone have a picture of how this is fixed in or know how it’s located??...

[cinquecento]

I've just replaced a broken gear box mount causing low speed vibration. It's unfortunatley difficult to inspect without the undertray and exhaust coming out..and even then it was hard to see.

[TVR Beaver]

I'm thinking its top of the engine, upper front type thing. We've even had it on the ramps, in gear turning the wheels, loaded with the hand brake, and my mate on the ungerside trying to find it. Nothing to report so not a mounting. It a c
kind of EEEk sound? not checked the dizzy, but it only does it for a second and its gone?...

[davep]

Harmonic balancer, may be worth a check.

[TVR Beaver]

It was new about 5K ago... its more of a dry bearing sound, but I dont think it is?

Does anyone know how the cat is held in the big front housing? It could be that vibrating. ties in with the temp bit and given rpm and maybe under load to some extent??