I have noticed while using RT in Active Shade mode, it stays noisy for awhile and then BAM, it jumps to a clean render. I have my denoiser set to 1. I am assuming the BAM is the denoiser kicking in, but for larger scenes, you never know when the BAM will happen. The VFB is set to, as a default, effectsResults.
Also, when I run RT, my MAX top left “3” button stops working.