I had a problem that sounded similar to yours and changing the transmission mount (it has completely collapsed, that was where the metal to metal sound came from) solved it. You can see it for yourself, look under the car and have someone put it in and out of gear. If it is the mount you will see the trannsmission jump up and down. The mount is inexpensive around $50.00, and easy to change. If you change it yourself make sure to jack the car up securely.
It could also come from the flexdisc (or flexible coupling if you will) on the driveshaft. Also easy to see, go under the car and turn the driveshaft with your hand. Look at the doughtnut shaped rubber mount on the driveshaft (there is two, one at the front and one at the rear). If it is worn you will see. I had it changed as well, it was making the noise similar to what you discribed. Also inexpensive, under $100.00 I beleive. Now I come to think of it it is more likely the flexdisc.