noise with Arnold Render

[fortsts]

Hi I'm using Arnold Render and I set the the sample of the lights in attribute editor/ Arnold very high like 4 or 5. But there's some noise on the stage(under the cube) that I cannot eliminate. BTW, the cube is an illuminated object and I set the sample 6.
Does anyone know how to make the noise disappear?

http://i.imgur.com/pcVtkr8.jpg

http://i.imgur.com/o6REYLx.jpg

Also, it takes about 20 min to render one frame. but it's not a very complex scene.

I'll be very grateful if anyone can help me to solve the problems.

[Gen]

I've use Arnold only briefly so I'm not sure but that noise looks like overly bright pixels. Check your light intensity. Have you checked your AOVs to see what element of the image this is coming from?