Don't know whether this has been covered before but thought I'd post a recent repair just in case it was of any use to other members:

Some time ago I noted under acceleration I had what can only be described as the sound of two scaffold poles banging together (which seemed to be under the car) after much investigation and head scratching I have discovered that one or more of the orange gaskets on inlet manifold was leaking under pressure.

So yesterday we set about replacing said gaskets and I'm glad to say this has fixed the issue, don't know whether these are considered a service item that are supposed to be changed periodically but if you get similar might be worth a look.