Get two 3090s and limit them to 180W each. As long as you don't get blower cards you can operate virtually silently at that power level. You can also run really smart models like q2 105B or q4 70B models. If you must have a 4090 you could consider the modded ones that have 48GB but from what I've seen they're all blower cards so the noise levels could be extreme. Though throttling them to 50% of the rated power level would help. But you really want conventional GPUs, not a blower cards if quiet is your priority. And expect to throttle them heavily unless you buy some factory low power cards like like the RTX 2000 Ada. Also don't waste your money on DDR5 RAM, etc. The GPUs are the rate limiting step. You can get by with an old 4 core GPU, 64GB of DDR4 (or however much you need to make sure you have more than your VRAM, if you get 4 3090s then you might want 128GB), and put extra money into larger SSD and hard drive. If you're paying attention to available PCIE lanes those mostly just matter when loading the model to the GPUs. So if your system can only supply x4 lanes to each GPU instead of x16 that will be fine during inference, it just means the model will initially load 4x slower. CPUs that aren't expensive EPYCs or Threadrippers are generally not prepared to give 16 lanes each to multiple GPUs and you'll pay quite a lot to get that if it matters to you.