Newbie question alert!

When I am accelerating (only above 4000rpm) I hear a 'click' from behind me (coming from the engine compartment obviously). There is one click when you put the power on, and another when you lift off. Doesn't happen if you rev the engine when stationary (the neighbours love me I'm sure!).

The power delivery feels fine, incredibly linear like it's meant to be (although I know peope rave about the sound changing when the VTEC kicks in, I must be bit deaf, because it doesn't sound that different to me, just louder and faster!)

Any ideas guys?

thanks

Robin

(PS I MAY have some news re OEM tyres in the next couple of days! Watch this space!)

(Also Hats off to Mark at Dali, new OEM hatch and trunk gas struts and clutch bearings delivered very promptly and MUCH cheaper than Honda UK even after shipping - Thanks Mark)