Hmm, that sounds like it should be checked by a dealer regardless. It probably is valve tapping.. From what see it seems to be a "common" issue with the VQ35..
this link looks a little better, http://my350z.com/forum/engine-and-driv ... stion.html
In it I saw towards the very bottom:
"Originally Posted by Weq View Post
Did anyone ever find an fix to this problem?
Just over 100,000kms and i developed a ticking/tapping noise from the rear drivers side. This noise only happens when hot and gets faster with revs. Starts at about 2000~rpm..
Ive run Motul 8100 (5w40). Did an oil change about 4000km ago."
With the response being:
"The rear driverside what? Closest to the firewall?
Put your ear up to the valve covers at idle. Dont burn your ear off! Have someone sit inside steadily rev the motor a little. You should be able to pinpoint which valve it is with just your ear.
And if the sound gets louder when you put your head under the car, like under the driver seat. Then it's probably your clutch. : ) My clutch chatters like a mofo. pos
I check my oil levels once a week. fyi"
Hope this is closer, if not, sorry i couldnt help =S