I bought the TipTop Audio - Fold Processor and while testing it, I discoverd, that without an input signal and when I turn the "Inject"-Knob there came some noise on the out, not very loud, but absolutely audible and a little bit anoying.

My question is:
Is this a normal/default behaviour or is it a production/manufacturer error?

Because, if i send a signal thru the Fold Processor and I have an unfavorable "Inject"-Knob position, the noise is clearly audible in the input signal on the out; on another position, it is there is no noise audible, but I think this may not be valid behavior.

Please help me out.

Thanks in advance.

Normal, actually. When you turn the "Inject" control up, you're adding a DC offset to whatever signal is there. And if there's no signal present, the wavefolder is trying to make something out of the DC offset...which is what you're hearing. The key to avoiding this is to keep the "Inject" down for most uses, unless you're trying to shift the waveform above or below the zero-crossing line. In those cases, that would be when you'll use the DC offset to "push" the waveform to where it needs to go.

Also, some fairly aggressive wavefolders can create waveform deformation to such a degree that it would SEEM as if there's noise present in the signal, but the issue really stems from some sort of very tight and very high-amplitude "scrunch" that's going on in part of the waveform. Ultimately, the "fix" is to simply note where the "don't" position is on the "Inject", then don't put the knob there...unless you WANT the noise, in which case...

Thank you @Lugia for your detailed answer.

Just so that I understood everything correctly:
It is normal that the "Inject" button produces this noise at the output when turning it?!?

Because if there is an input signal at the "in" (e.g. a simple sine wave) the identical noise is also produced at the output (when turning the "Inject" button).

Thanks in advance.