I ran BOINC on my 15" MBP (2013, with 16Gb of RAM) and never had any issues with it.

I bought a new MBP (2019, with 32Gb of RAM) the day they became available to the general public, and I "restored" my 15" contents to the new laptop.

Had to re-download and reinstall the SETIatHome package for some reason I've forgotten.

The fan runs CONSTANTLY when BOINC is running, on the new machine. It NEVER ran (or at least it didn't run so I could hear it) on the old machine.

When I shut down the BOINCManager, the fans stop running (at least audibly).

Does anyone know what's going on with this?

When I shut down the BOINCManager, the fans stop running (at least audibly).

Does anyone know what's going on with this?

The surprising thing to me is that the fans didn't run audibly on the old machine. As BOINC will depending on your settings run all cores of your CPU flat out, I suspect without the fans running you would run into some serious overheating problems. On my laptop under Linux for the fan to go completely silent at the moment I need to restrict BOINC to one out of four cores. Two cores my other half can't hear the fan without her hearing aids and it is quiet enough that if I am not paying attention I don't notice it. Currently I have it running on all four cores and can hear it above the sound of my desktop's fans. However that is still quieter than it was on two cores when during the summer ambient temperature was above 38C!