I think your question arises from a misunderstanding of the conception of noumena in Kant. The noumenon (from nous, thought) is not an existing world out of reach. The thing in itself is a thought that has a methodological value, you could see it as a mental experiment, though this might be misleading. The whole idea is, as poorly as a few words can render it, that when considering all that can appear (i.e. all objects that can be given to a sensible intuition) as bound to the forms of our sensibility we are, logically, also cosnidering our thought as different from the objects that it thinks: the faculty that gives objects to thought isn't thought. Though that is clearly the case, at least the way Kant see's it, it isn't obvious that this is the only possible subjective order of faculties (i.e. we do not know the determining reason to account for such a subjective order of faculties). THis is exemplified by the possibility to think, though only in negative, of a different faculty, i.e. an intuitive intellect, that produces by itself his own objects of knowledge.
So: noumena is not a thing, (usually it is thought of as external thing, but that "external" makes the absurdity of the interpretation very clear, as it bounds it to the form of space). In asserting that my intellect is discoursive and it's objects are given to it by a sensible intuition I specularly determine a negative representation of a subject that has different faculties. How? By simply denying it my faculties. What is the definition of intuitive intellect? Well, that which is not discoursive, that which does not need a sensible intuition to provide objects: that which does not need judgment to gain knowledge. It's just part of the critical method, you need a restriction to account for the legitimacy of the assertion, that doesn't mean that you have to positi the existence of something out of those limits, moreover that is exaclty what Kant is trying to avoid, that we go on to determine something outside of the limits of possible experience.
If you think it through you will find that both denying and asserting the existence of noumena leads you to contradictions. There is a reason for that. Noumena is just the thought, unavoidable, of the non necessity of the faculties of the subject. I did not say contingency, and there is a reason, it's not something you can go on and search for it's determining reason. It's just a limit.
A subject with X faculties cannot account for his X faculties with his X faculties, for as soon as he considers that his faculties need a determining reason he considers them as contingent, hence every solution he can posit is going to be thought as bound to its own contingent faculties. Noumena is unavoidable for this very reason. It's just the rendering of a limit.