my 1.8t makes a funny buzzing noise on start up when cold. goes fairly quiet when warm but is still there. sounds as though its coming from under the intake manifold at the back. its changes with engine speed.

can't put my finger on it. I'm pretty handy with engines so its not the obvious things.
car runs as normal no issues at all.
sounds abut like a noisey injector but its not.
any ideas before I start pulling bits apart.

no codes or lights.