Anyone elses MK2F SPI throttle body buzz/ rattle?

Been having some slight issues with idle on my polo for a while now. It just wont settle down to a smooth tickover. Its not drastic but it is noticeable and annoying, as it vibrates causing all kinds of buzzing and rattling. Its at the point now where I hold the revs over 1000rpm when sat in traffic to stop the vibrating. Tried changing the usual easy suspects. Plugs, leads, dizzy cap, rotor arm. Made no difference. Went under there today to try and locate the worst buzzing noise and try and at least stop that. It was the 6N engine cover I fitted.

So, to the point. While there had a listen and the Throttle body makes a buzzing/ rattling noise, loud enough to hear with the bonnet closed. Starting to think that this may be something to do with the idle problems. Does anyone elses do this? as i'm sure my previous SPI didn't.