Whining noise from gear shifter in Mondi t

This is for a Mondial t...

The sound is like a whining sound, almost like having a bunch of loose washers on a screw and shaking it VERY lightly.

I noticed is is not a function of which gear is selected, but that of RPM. It was prominent in 3rd gear in the upper RPMs. On the highway, I noticed that if I freewheeled in neutral and revved up to 5-6000 rpms the same sound occurred.

It comes from the stick shifter and I cannot figure where it comes. I suspect it is a resonance that comes from the gearbox, up the cables and resonates in the gear shifter.

All gears work perfectly, 2nd is a bit tight on a cold start, but everything is fine at operating temperature or above 4000 rom. No clicking or chattering at any shift or RPM range, clutch engages properly, engine runs fine etc.

I changed gearbox oil 2 weeks ago (noise has been there for over 6 months - since I got the car), it was a tiny bit cloudy, but of the correct "motor oil color". The magnetic plug had a slight layer of "peach fuzz" on it, no large chunks or anything - I therefore don't think it is a problem with the box.

Is there something loose in the shifter assembly? Am I using the right box oil (4.7 qts of Castrol 75W90 / GL5)?

This the only prob with the car.

Marco