the motor only makes this sound when in gear in the water, I changed lower unit oil and there was metal shavings in oil.
Metal shavings are commonplace in lower units, in fact the drain plug is usually equipped with a magnet to collect these guys. A little is ok, but if you pull out a wad of filings wrapped around your magnet, like the end of a Q-tip swab then you have something wrong. Course how long has it been since the oil was changed? The longer the more would be normal.
When exactly do you hear this noise and at what engine rpm? Is it present at around 650-1000 and leaves above that, or is it present all the time? Is it a constant uniform noise or is sort of random in the type of noise it makes? What type material and pitch are you running on your prop?
Reason for the questions is my 90 had what's called "clutch dog rattle" when I ran my high per. 24P SS prop. It only occurred in the rpm range I mentioned and if I put a lesser pitched prop on, like my 21, it wouldn't do it. Not uncommon in 3 cyl. engines.
Mark