Ever since I've been able to use VTEC (i.e. after the 1st 600 miles) I've noticed that after some enthusiastic driving, the engine can occasionaly take on a bit of a rattle when in VTEC and full throttle. It was particularly noticeable yesterday - after maybe 5 or 10 minutes of hard driving, mainly on VTEC, the rattly noise appeared - only on full throttle in VTEC.

It kinda sounds like it may be the exhaust heat shield or possibly even knock, in which case the knock sensor is doing a pretty poor job

Power delivery is normal and there are no odd vibrations, but once it has started, it will do it consistently in a given driving session but dissappears if the car is left for a few hours which makes it sound heat related - it worries me that a hot spot is getting generated in one of the cylinders giving rise to knock. The car has only ever been run on optimax.

Anyone got any ideas or experienced similar?

 

I've had an identical experience. It did disappear for the last 1000 miles but has recently made a return (perhaps now that it's colder? No clue) I'm currently on 3800 miles. I found that it would be a rattle/quick knocking noise which seems to come from the center of the dash, and will remain between 5000-7000rpm for quite a while when throttling.

 

Had this with my original S, turned out to be the gear lever rattling, you can check by applying some pressure to it while in VTEC mode. If it cures it or reduces the noise then that's the cause, your dealer will adjust and add some grease to the base of the lever, a 20 min job.

Heat shield or other could be the cause, but more difficult to suss...

Good luck!

 

Had something like this on an old Del Sol Vtec I had. Not that I had a heavy right foot in those days , but things used to rattle when it hit the vtec, and it was a constant battle with the spanner. But after owning an Elise before the S2, I am immune to the sound of rattles, squeaks and grating noises.