Hey guys. Really interesting thread for me, I had to deal with the exact same issues as the OP. Changing any settings- from lighting, sampling, or GI processing- didn't work, regardless of what I did. However, I think I found a solution when having to deal with an interior scene that had many glossy and reflective materials. Some of the materials were creating a huge amount of noise, regardless of the sampling I used.
I found a solution for this issue online- for each reflective Vray material in the scene, I went to its options rollout and set 'treat glossy rays as GI' to 'Always'. The noise disappeared; and together with the 'denoiser' option this meant that I got a clear, noiseless render without having to tinker with any other settings. The funny thing is that the bright spots created after applying the Vray lens effect to the render also disappeared when doing this.
I have to test this in other scenes as well; but people dealing with the issue mentioned by the OP might want to try this solution and see if it works for them.
