Script mentioned below brings only the data that has the combination > 1. I hope you can take it forward from here to avoid data duplication using the timestamp or anything specific to your requirements. Does it help?
LOAD DISTINCT MemberID, CustomerID, COUNT(MemberID&'_'&CustomerID) AS Count FROM (SourceFile.xls ) GROUP BY MemberID, CustomerID;
LOAD MemberID&'_'&CustomerID AS Key RESIDENT Temp WHERE Count >1;
DROP TABLE Temp;
LOAD * FROM (SourceFile) WHERE EXISTS (Key,MemberID&'_'&CustomerID);