When using Renoise versions less than 2.6, there is a buzz in Aalto's output at some buffer sizes or when rendering to disk. There are two ways to fix this.
Use compatibility option in
Renoise: Click on "?" in the instrument panel, then enable the "Static
Buffers" option, which will buffer and drive the plugin's render function with
256 samples - always.
Get a beta of Renoise 2.6.