Buzzing typically indicates incompatible bulbs. I couldn’t find much spec-wise from Belkin, but I’m guessing the Wemo is a Triac dimmer. If that’s the case, you really can’t compare a WiFi Triac dimmer with a Zwave Mosfet dimmer. They’re completely different.
Unfortunately, not every LED bulb works with every dimmer. That’s just the way it is. To quickly insure your installation is correct and evaluate the bulbs, temporarily swap out for incandescent bulbs to see if that resolves the issue.
Take a look at the bulb compatibility list. This is a work in progress with a replacement Wiki coming.