[skykng]

Unusual to have the loop halfway inside the cabinet -- is that factory? Can you move it to the back? Can you place the loop outside the cabinet to see the effect?  My guess is the loop is interacting with the converter or the IF amp - loktal tubes - see if a shield over one or both those tubes does any good.......Verify all component grounds are solid.   Are the loop antenna leads correctly connected?  Good luck.