it sounds more like injector clicking to me. I'm certain it is not the VTC that is making the noise. When activated, there just isn't any way they can make noise because oil pressure is pushing against everything... it's like a hydraulic cylinder at full stroke and the VTC's internal moving parts cannot move in this situation. You may be hearing something that is oil pressure related, since when the VTCs are off the system is bleeding oil pressure out the back of the intake cams. When the VTCs are activated there will be a slight increase in oil pressure which might manifest a noise somewhere else or change the tone/volume of an existing noise. Your original post mentions the noise happening between shifts while at med/low-RPM driving - have you tried driving with the VTC activated full-time to see if the noise remains?
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