HDRI + Glass Noise

Hello.
I have a very simple scene in Blender.
It’s just a simple glass with subdivision modifier applied and HDRI environment texture. Nothing else, no lights, no more geometry. When I render it there’s a noise.
How can I remove it? This image is made with 1000 samples and it took about 1:30 to render. But even with 6000 samples the noise is still there (and render time is about 6:00 minutes).
I did the same scene in Modo and Lightwave and the render times are about 25 seconds and no noise at all…
Any hints?
Thank you


Do you have multiple importance sampling enabled in the world settings? That should help reduce the noise.

Well, I didn’t have it enabled.
However, when I enabled it, nothing has changed. The same amount of noise is still present in the render.
When I try to rotate environment HDRI texture the noise also changes but never dissapears completely.
It seems it’s the problem of 3rd+ bouce of reflections / refractions, those areas are noisy.
I don’t know what to do with them, so I’ll probably wait until some cycles update.
Thank you for your advice.

Change your Clamp settings to 1, in your render panel.