I just felt it again and it starts right in the corner at the bottom.  What the heck would cause this?  When my skimmer crapped out, I was able to deal with it without moving the sump.  It hasn't moved in a year and a half. And there's nothing behind the sump except wires.   
 
Just perplexed.... 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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