I believe the effect that you see results from overly sharp scanned negatives. Once you go above 3000 horizontal pixels, then you scan grains and also the void between grains. Then it is easy to over sharpen them in one way or the other. Some people say, DXO does a good job with its simple noise algorithm. I try this out at the moment: I processed 400 negatives in LR for a photo book. Exported them as JPEG and send them away. The photos in the book looked ugly. I got in an argument with the print company. They said that LR over sharpens the JPEG (true, I had LR on the lowest sharpen level while exporting) and that their own algorithm does "the rest". It was my fifth photo book project with the same company, previously I did not process the scans or had processed raws. They allowed me to send the photo book back and will print a new one with reprocessed photots. I am busy now developing the same scans in DXO. I hope that it gets better.