make sure your capacitor is rated for 5 Volts or higher. Any less and you will get that hum too. A 10volt one I've found works well. Also make sure the cap is in correctly. The side of the cap with the different color stripe and the (-) signed in the negative. Connect this side deiectly to the speaker. Next connect the oposite side of the cap (+) side without a stripe) to the (+) output of the lm386. If the cap is in backwards, the result will be a humor no sound at all.