drain your MTF fluid through a cheese cloth if you can't find an auto store that has a specific paper funnel with sediment screen. Look for brass or gold peices once strained through. A tiny bit is acceptable, any chunks are unacceptable. If there is a bit of "dust" it is not a big deal. First things first lets get that MTF fluid inspected and changed.

So the grinding noise is when the car is ALREADY in gear? If so I would say it is NOT synchros.

 

Are we sure that the grinding is coming from the tranny? Or does it sound more like a very fast rattle?