I heard that today too.

 

Most likely you are just hearing the valves 90% of 400ex's have this problem with "Ticking" noise. Its very common. You could check your valves and ajdust them if nessicary but even when in specs you will still hear the ticking its just hit or miss with them. If you visit www.exriders.com you will see about 100 threads about this.

 

Having a slight problem with my 400 ex just changed my sprockets and chain today all was good until a half hour into a trail ride session my axle is making a rattling noise there is no play in the carrier checked that already it seems to rattle bad after second gear and when slowING down most of these online forums keep saying carrier bearing can anyone help?