First this is not entirely true, the PS4 is not loud because it's overheating, it's loud because the cooling system is loud when cooling down the machine. Should the PS4 have a better cooling system, it would still produce heat, the better cooling system would do the same as the current one is doing but you simply wouldn't hear it or you would hear it but not as much as you hear it as it is now, but ONLY if the improvements are geared towards correcting the noise.
In fact the PS4 does not overheat PRECISELY because the cooling system won't allow it to happen at the price of a noisy process. Should it actually overheat, it would stop working altogether and your TV screen would go dark.
Every machine out there that works with processors produce heat (PC, Consoles, TV's etc.) Therefore every machine out there needs to be cooled down. It's how you cool it down that makes the difference in terms of decibels.
Anyway my point here is that I'm not fully sure we should get too enthused about a noiseless cooling system cause that's not mentioned anywhere. People are simply assuming that Sony is tackling the noise when in fact they could simply worry that the much more powerful PS5 could ACTUALLY overheat and therefore they are putting more money to ensure it does NOT overheat and for all we know it will be very noisy. Efficient in preventing overheating but still noisy...
I'm not saying they won't do something about the noise either. It's also possible that they'll tackle that issue along with the heating one. I'm only saying don't get too enthused cause dealing with the noise issue is mentioned NOWHERE, it's only an assumption.