I was just going to post a similar question. This is on a 99 V70T5. At 1100-1200 RPM, it makes a noise that is very hard to describe, it is metallic and sounds like a cross between a loose catalytic converter heat shield, and a pulley just barely rubbing against metal, with a touch of bearing noise thrown in.

Using a stethoscope, it cannot be heard anyplace other than the timing belt cover, which makes me suspect it is a failing bearing on the timing belt idler pulley or on the timing belt tensioner. It could possibly be the serpentine belt tensioner idler, which I can't safely reach with the stethoscope, but I do not hear the noise when listening to the alternator or power steering pump. (I'm not sure that means anything, since the noise would have to travel along a rubber belt to be heard at the PS pump or alternator). I am also curious about why it goes away above 1200 RPM, rather than getting worse.

The car only has 73,500 miles, and I had hoped to wait for the factory recommended 100,000 before doing the timing belt.

Is there anyone out there who can confirm or deny a relationship between timing belt roller bearings and a noise like this?