Rack server heat & noise greatly exaggerated?

I recently started playing around with a pair of old refurb Proliants. I have Proxmox for various internal services (DNS, VPN, NAS, DB, Media etc) on one and windows server on another to play with AD and host some dedicated game servers. I am probably going to put windows on a VM too.

Except for start-up these machines run surprisingly quiet and throw far less heat than expected. The windows machine runs near silent. The proxmox machine is a bit more audible but both of these are racked about 6 feet away from my desktop and they produce a mild hum at most. By no means the jet engine I was warned about. Same thing for heat. Feel like they don't kick out any more than my desktop does when rendering and temperatures are stable on both servers.

Are the noise/heat disclaimers coming from pros whose experience with these machines are running full bore in enterprise environments?