Hello new to this forum I have a 1998 z34 It came up with very loud whisle noise in side the car mainly at highway speed all so when you turn on heater to. is there a body vent or some thing that might be causing this ? if you crack a window or sunroof it pretty much stops any help would be great. buy the way shes got over 180000 miles on her and still going strong

 

Welcome to the forum. Is it coming from a bad door or window seal possibly?

 

Not sure they all look real good It is like its building presure inside the car and if you turn on heater it really do's it and it gets louder when you change fan speeds

 

I suggest checking your heater/defrost vents...under your dash or on engine firewall (?)
When you switch from one source to another it could not be closing the vent all the way & could cause a whistle (?)

Whistle while you work - YouTube

Above a tune to listen 2 while you work/search for your Whistle Prob.
Good Luck on finding the source/prob

 

do you have any idea where there might be located ? I know on the the firewall lol

 

you would have to pull the dash off, there might be a gap inbetween the dash cover and underneath the dash causing a whistle like noise