You could try fan swaps and sound dampening but it can easily end up costing more in money and time researching compatibility than what some of these servers are worth.
Starting small is what I recommend. I had a rack before. Now I just run mini PCs.
Cheap mini PCs have been my goto.
They are often powerful enough to get the job done, small, low power, quiet, and are easy to ship to sell if I want to upgrade. They may not be as reliable but I did the work on the software side to be able to easily replace or add new nodes.
I've been downsizing.
A few years ago I had three Xeon E5 rack servers with 64GB of RAM each and a bunch of HDDs.
I then cut it down to three mini PCs with 16GB of RAM each.
Just recently I cut it down even further to just my single Linux desktop running Kubernetes in the background.
Why? I realized that my interests are all on the software side and more hardware doesn't contribute much to improving my experience either building or using the lab.
I also tend to make improvements in my software stack when resources are more restricted and my lab became so much more reliable and efficient over the years.
I would do pretty much what I do now with two mini PCs and my desktop PC running background services in a three node cluster. I change my mind too often though and just did a bit of a rebuild over the holiday, so by next weekend I may have a completely different goal.
I having considered replacing the desktop with a laptop for more portability.
I would also not mind getting a 2.5 Gbps switch. I have all 2.5 Gbps devices on the network except the switch which is a little silly.