A small percentage of the users have experienced hum, especially with turntables without a separate ground wire. Here are a few tips on how to get rid of it.
Sometimes the source of the hum is external. It could be that your Muffsy Phono Preamp sits directly over a power amp's transformer, directly below LED lighting, or that the AC wall adapter sits next to another noisy power adapter.
Moving the phono stage around, turning off other electronic appliances and lights could help you find the source of noise. If this doesn't help, the source is most likely not external. See some of the tips below instead.
Most turntables have a separate ground cable which NEEDS to connect to both the turntable and the Muffsy Phono Preamp:
If the ground wire is connected and you still get hum, have a second look at your Muffsy. Make sure that all the RCA connector grounds are connected, and that they are connected to the ground screw:
Your turntable delivers a very low output signal, and is vulnerable to interference. Make sure that your signal cables are of the shielded kind.
If you've tried everything and the hum persists, consider using the enclosure for shielding as described in this blog post.