I've got a '95 CB400 Superfour FIII. It's developed a noise that sounds like it's part whistle, part vibration, but It only happens at 7,000 RPM. If you cruise at 7k the whine is constant, if you accelerate past 7k it happens very briefly. I thought it was due to a hole in the exhaust, but having spent yesterday welding and repainting it, it's evident that it's not the cause.

With the exhaust repaired, the engine noise is now obviously reduced, but so is the whine. Presumably, it's coming from the engine, otherwise there'd be no difference in noise level.

A few months ago I took the engine to a local mechanic to have the valve clearance set on one of the cylinders; it was practically down to zero. I don't know if this could be related, but it had crossed my mind that it could be an inherent flaw in that valve, or maybe a problem with the cam chain if it hasn't been correctly adjusted.

Can anyone help.


Cheers.

Does the noise happen in all the gears and at the same engine speed?

Yeah, pretty much. I guess it's probably nothing to do with the gearbox.

Oils fine. I'm not loosing any and it's clean.

Weird.

Don't cruise at 7000rpm