E30 Zone

The rev rattler is an irritating creature that lives under my car and only comes out on hitting 300rpm. He tends to go home again after about 5000, but has been known to stay out later. The noise doesn't happen when sitting out of gear and revving so I'm guessing it must be gearbox related. I've checked all gearbox mountings and the exhaust bracket and manifold gasket but they're all tight. Its quite a metallic rattle, like a loose clamp which is what made me look at those. The only thing I haven't checked is the gear oil level (incidently, what's the allen key size?), but if its low surely the noise would be present throughout the rev range? I need any input possible to rid me of this foul creature.

Comes out at 3000rpm, not 300rpm, dur.

Is the exhaust anywhere near the bodywork? It could always be catching somewhere? If its banging up against the underside somewhere, it would sound metallic.

Does it go away if you hold onto the gearstick?

I looked over the exhaust and it doesn't seem to be that, and no it doesn't go away if I hold onto the gearstick. I've also noticed that its not there straight away when I drive the car in the morning, which is making me still think that gearbox oil might be involved as it'll be thicker in the cold. Does anyone know the allen key size for the gearbox check and refill plugs?

17mm

if it's really loud I would be hazarding a guess at the gearbox exhaust mounting