I thought I read awhile back if a volvo part is installed by a volvo approved shop, the warranty on the volvo part is doubled in time. Might be worth looking into.
I have a 2003 VP 5.7GXI with an SX-M VP duo-prop. Exact same sounds at exact same time. Noise in neutral, when dropped into gear is smooth & quiet. It's been this way for 5 years. When the gear oil is cool, no sound is emitted. I have thought that this sound began after I tapped the bottom...