I've had that same sound a couple times, on random cold days.

 

That's exactly what it is

 

Check the starter mounting bolts for tightness. This is the most common reason for grinding noise...

 

Bit of advice for the new guy.... check the dates. This thread is over a year old.

 

I have 2 Subarus and both had same problem. Was lucky to find the noise with the starter already removed. Hope this helps!

I know post are old but people read these things all the time and never post anything. Just trying to help!