Adding items to ArrayList prints ArrayList index to the screen

When I add items to ArrayList, Powershell also outputs the ArrayList index to the screen. How do i prevent that from happening?

Here is my code:
 

$alComputers=new-object Collections.ArrayList
foreach ($child in $ou.psbase.Children) { 
    	if ($child.ObjectCategory -like '*computer*') { 
		$alComputers.Add($child)
	} 
}

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