Groaning noise when engine heats to fan clutch range
 

Recently replaced fan belt and idler wheel because engine made a noise like a big truck air brakes coming on. Good news, now it doesn't get into fan clutch engagement temperature as quick as before.
Bad news is when it gets above 222F indicated on scan tool, I get a groan that sounds like all belt.

Belt might not still be tight enough? Fan clutch failing? Any other relevant ideas?

BTW, replaced alternator a couple months ago and it seems to be operating right. A/C clutch is worn out and disconnected. Doesn't sound like the electric fan.

Stethoscope time!!

And in this day and age of crappy parts, NEVER rule out a new part that you have installed.

Solved the puzzle without a stethoscope or piece of garden hose!

After I replaced belt and idler pulley, I put everything back together and reconnected the electric fan. My electric fan has had a bad bearing forever and I'll be replacing the motor/bearing soon, so unplugged it and it's fine now.

Now I'm not sure about the mechanical fan clutch. When it's cold it has resistance, doesn't spin free, just moves about 1/8 of a revolution.

Normal. When cold, all the silicone fluid in the fan clutch settles to the bottom.