my old lump used to do it too, it sounde3d like a big end bearing for 2-3 seconds on start up, but i could still drive it really hard and had no trouble with it for 10k!!! and the engine is now in another car and its still going strong!!! all vtecs have noisey heads tho, all the b16's and b18s i have had have all neaded the valve clearence adjusting wen iv got them