>The Germans didn't have spies collecting rumors in the US.

Yes they did. https://en.wikipedia.org/wiki/Duquesne_Spy_Ring

This ring was broken up before the US was even in the war. Operation Drumbeat began after the Pearl Harbor attack at the end of 1941 but was most intense in early 1942. There was lots of Bund activity in the 1930s and prior to Pearl Harbor but very little afterwards.

But also, even if there were Bund spies in American ports was unnecessary and unable to provide tactical information to the German U-boats. Unable due to practical limitations of communication. Unnecessary because the US was so ill-equipped for the battle. For instance, the Bund wouldn't have been able to report on the movement of convoys because there were no convoys.

The US still had charted aids to navigation light up, and cities weren't blacked out allowing the submarines to sit off the coast and see US ships silhouetted against the city skyline behind them. A German submarine sailed into New York harbor using a tourist map as a chart!