I have six IBM 2U servers in my home rack (36U). They're really well-designed and the noise level is not too bad even in the room with the rack, but there is also a 1U SuperMicro server in that rack with two Tesla cards and it is so loud as to be quite annoying anywhere in the house. I keep it turned off unless I'm specifically working on it, which isn't how I'd like it to be. The lesson I learned is that bigger servers (4U would be even better) have bigger fans and run more quietly. Also IBM servers aren't as loud as Dell and Dell servers are quieter than SuperMicro. I'm thinking the next addition might be a cluster of Raspberry Pis.