guessing it was not making the noise before the oil change ?
how many miles on the motor ?
are the bolts tighten ?
if its only doing it at 4000 ? are u sure its the motor and not something loose on the bike ?
go to the zx-10r.net forums
repost this they are awesome and will help you out quickly.
i double checked the bolts today, i didnt find anything loose. it only seems to do it when your in gear and ya go above 4000+ rpms i was thinkin it might be the change from regular to synthetic. did anyone else have this issue? and i have just over 11000 on her know. thanks for any help or comments.