About a week ago my '90 740 b230F stated making this strange noise at startup. It is a somewhat harsh, aluminum can scraping against metal sort of sound. It follows engine speed and seems to show up at startup and when I'm stopped. But I can get it to go away consistently by bringing the revs up for about 10 seconds and it'll slowly fade. The sound comes in and goes out in the same smooth manner. Any ideas what this could be?

I've always had this 'extra blowing fan' sort of noise that came during startup, followed engine speed, and would progressively fade away after bringing the revs up for about 10 seconds. I wonder if they're related, and I wonder what this sound is. hmmmmm...