I think at idle the PS4s are slightly quieter than the PS5 but when gaming the PS5 is far quieter. At idle I think I hear ball bearing noise from the blower. Pretty typical for a BB fan. But I have yet to hear it change speed in any game and that is a huge improvement over the PS4, especially the noisy PS4 Pro.
The problem with the ps4 is noise levels over time. I made a lot of extra cash (or a lot of free meals depending on the person) by opening up ps4s/pros and cleaning out the fans sometimes repasting the heatsink. I did the same with the ps3 also.
Right now the ps5 in my house is louder than my xbox series x but its very slight and luckly i have zero coil whine in either system