Whiteblock whine
 

When five cylinder whiteblocks get up in the rpm range they make a distinct rather high pitch whine that increases with rpm. Maybe it's a dumb question but I can't seem to find an answer as to what's making this sound. Every i5 Volvo I've driven makes this noise.

Aside from the turbo, which I'm sure you aren't talking about, makers have to work hard to make the intake quiet. It can have some serious jet engine sounds coming out of it. Cams can also make crazy noise let alone simple gear noise from the tranny.

The 5, in my opinion, is an all-around strange engine. I like strange. But it is not what I'd call a smooth engine. To me it almost groans when it revs. It is noisy. I bet the noises we both notice are simple resonance within the aluminum. Nothing like the old cast iron to kill sound.