The main original source talking about the Golem was the Niflaos Maharal published in 1909. It claims to have been written by the son-in-law of the Maharal (R' Yitzchok Katz) and was kept in the library in Metz, until (after being in the hands of some middle-men) it was discovered by R' Yudel Rosenberg of Warsaw. R' Rosenberg claims that the Noda Biyehuda went to the attic where the Golem lies (although he asked ten of his students to say Tehillim for him at the time, because of the danger).
However, (R') Shlomo Rappoport says that the Maharal never created a Golem, and the stories are forgeries.
R' Shwartz also mentioned a proof to the fact that the Maharal did not create a Golem, in that no Rabbinic historian of his time mentioned the Golem. Neither the Chida nor the Tzemach Dovid (who was a student of the Maharal and wrote a sefer on Jewish history) wrote that the Maharal made a Golem.
However, R' Shwartz points outs that the ֲBnei Yissochor wrote that the Maharal used to use Sefer Yetzira (the Kabbalistic work discussing the creation of Golems) and the Imrei Yosef (the Rebbe from Spinka) quotes the Niflaos Maharal (obviously being of the opinion that it's a legitimate sefer).
Moreover, he writes that it in Megilas Yuchsin (written and published in 1864, some forty years before Niflaos Maharal) that the Shoel Umeishiv (who was alive when this sefer was published) went to Prague and wanted to go to where the Golem lies. The Gabbai told him that before the Noda BeYehuda went up there, he fasted and went went to Mikva, then he wrapped himself in a Tallis and Tefillin and went up. When he came down, he said that no one else should go up there.
So R' Shwartz answers that it's possible that the Maharal created this golem for a short period of time and then destroyed it. However, people made up rumors about it.