I am having this same issue, though it is reflections on the surface of the glass. No mater what settings or the amount of samples I select, under ray tracing translucent or raytracing reflections, its like the denoiser is excluding all the glass, or the sample count is bugged on glass/translucent objects. Ive tried thin translucent, double sided, different lighting modes for the material, etc. Its always the same noise. If I switch the material to opaque, then the reflections become smooth and nice as Id expect. Am I missing some hidden check box, a limitation of translucent materials or is this a bug?