Is it like "da da da da" sound? if yes, it may be the valves tapers. it is a gap between the taper and the valves. It may be fixed after changed the engine oil (or thicker oil). I am not 100% sure on Honda Engine. I owned a Ford Laser before and all Ford's have the similar problem. I would suggest to check the engine oil condition immediately. because if it happen while you driving, the valves and tapers will worn out quick. keep your engine rev as low as you can. Thanks