I've had this issue (during and after GPU-intensive tasks, which aren't common enough to be a major nuisance), and after blowing compressed air through all exposed vents, didn't notice a change. I should schedule a repair time at a retail store to see if that fixes the issue.

A jury-rigged stopgap that is surprisingly effective for me is setting the metal-bodied laptop on top of an liquid icepack for a few minutes. kernel_task drops to background noise and I can continue working.