5000 rpm transmission noise. Please check yours as nissan says its normal

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Hey guys I need your help as I'm having this loud grinding noise coming from my shifter including vibration at 5000 rpm and above. So I had a specialist come out to deal with my peeling paint and this noise. I took the shop foreman and the specialist on a test drive and they agreed it was abnormal. One week later I get my car and they now claim all 370z's make this noise and that it's normal and that to drive the car at this rpm will damage the engine and transmission. I think that is completely wrong and before I drive 60 miles to find a dealership with a 370z with a manual transmission i want your opinion. It only occurs at 5000 rpm and above and if you move the stick I diminishes. It comes and goes but they won't fix it. My only option I see is going to another dealership and making them test drive both cars to prove that it is abnormal. Does your Nismo make this noise? Also with my paint peeling from the Nismo body kit anybody else have this issue besides the few on here that i know about. Thanks for your help.