EC2 EBS usage different between two instances

Question

I have two Windows instances with the standard 30G EBS drive.  They were created from the same AMI.  After some runtime, one instance shows 27G used space and the other 15G.  I have manually gone through and looked at the properties of all of the directories on the drives and they are basically the same.  I have manually added up the size of each directory on the full drive, and it totals about 15G - not 27.  
So my questions is, I have one drive that is hiding 10G somewhere.  How do I find it?  I ran the disk cleanup tool, but it only found a little.

Answer

Finally found it.  It is windows defenders scan files.  One instance only has the files for today, the other has them for as long as the instance has been running.  Not sure how to fix that yet, but this question is answered

EC2 EBS usage different between two instances

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