Did you replace the QR skewer on the rear wheel with the one that came with the Tacx? The Tacx QR is designed so that when you adjust the rear end of the unit it fits snugly around the QR.
I presume when you fit the bike to the Tacx you take up the rear slack with the adjuster, and then lock it in place?
What about the contact with the wheel? I presume yours is like the Excel I used to have. You can adjust the pressure of the roller against the tire. It needs to be firm enough to make good contact, but not so tight that it presses hard against the tire.
After you've fitted the bike onto it, check for any looseness at the rear end. It should be completely rigid.
Check the roller without the bike fitted. Spin the roller by hand. There should be no detectable movement if it's running nicely on it's bearings.
I'm being a dimwit here, but the rear wheel is fitted correctly to the dropouts?
You will hear noise from it when spinning along but that should just be tire noise. It it's buzzing, then I wonder if it's an electrical fault? I don't know the one you have, but my Excel was mains operated as it had a feedback between the rear end and the pooter it used that you fit on the bars.