In my home recording setup I am using a laptop, connected via USB to an external sound card, which in turn is connected to a set of nearfield speakers. After upgrading my laptop I started experiencing disturbing noisy/crackling sounds on the speakers (but not on the headphones), even without audio playing.
As it turns out, this was caused by a ground loop, from both the laptop power supply and the nearfield speakers having grounded power cords.
After doing some online research I came across the Behringer HD400. It is now installed in-between the soundcard output and the nearfield speakers, and with this, the ground loop problem is completely eliminated. I am very pleased with this result.
The Behringer HD400 is compact, relatively cheap, and does exactly what it advertises: eliminate hum and break ground loops. The housing looks solid.
As always, the Thomann service was great, with prompt shipment and very fast delivery to the Netherlands.