(thanks for your reply) So even with universal settings, could I try upping the subdivs on a problematic mat or light? I did actually try this a few days ago: setting the subdivs on a problematic (light coloured) wood material progressively up to 1000 made no visible difference but did negatively affect render times. Maybe the lights were the problem though.
On the noisyness thing, it’s not that other materials are noise free, more that you don’t see the noise as its hidden by textures ( I think anyway)