I just sent this question off to the boys, but eveyone desrves a shot at it.
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My beloved wife drives a 2004 Nissan 350Z roadster. The car has a 6 speed manual transmission.
When the ambient temperature in under 45 degrees, upon cold start in the morning, the car makes an ungodly screeching sound under acceleration. The sound appears to come from an area on the passenger side of the dashboard/firewall area.
The sound miraculously disappears when the car has traveled about 2 miles, and has started to warm up.
Being a die-hard motorhead, this is driving me completely nuts. The first time I ever heard the sound was after the dealer from whom I purchased the car changed the gearbox oil when the car had about 24,000 miles on the clocks. This may be significant, or it may just be useless information.
I’ve (the dealer) has done everything short of replacing the car. Belts and tensioners. Clutch throwout bearing, bushings and clutch. I suspect something like a bad planetary gear in the gearbox, but try and talk a dealership oil change tech into that and you’ll see my problem. I’ve done my obsessive googling. I can see evidence that ‘they all do that’ =8-o but noone can tell me what it IS. Some dealers have even replaced the entire transmission under warrantee, and sometimes the noise even went away. (!!)
can anyone tell me for sure what the H-E-double hockeysticks is going on here. My wife loves this car as much as it is possible to love anything inanimate, and its sending all involved around the obsessive-compulsive bend.
Get a section of garden hose, maybe three or four feet long. Use it as a stethoscope to find the source of the noise.
a great idea, if the car did it while it was stationary. 
the notion of crawling around under the bonnet at 45 per is most unappealing. 
Have you tried driving the car without the heater blower on? I’ve heard blower motors make a screeching sound until heat starts passing through them. And if the shaft bushing in the blower motor has enough slop in it, it could be effected by acceleration.
Tester
It could be a vacuum leak. Does this car have an oil-air seperator in the PCV system?
vacuum leadk is something i hadn’t considered… time to do some poking around under the hood and checking lines and fittings…will let cha know
thanx
g.