Small Grey line at the bottom of Screen

[xaero26]

I have a small grey line (translucent) line the bottom of screen
The line goes away when I hide my dock or go to a full screen application like parallels or Dashboard
Anyone knows what it is and how can I remove it.

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[poiihy]

This is your image:

 

[xaero26]

Yes, you can see a Grey line right below Trash