Maybe you should put a yoga mat inside your keyboard.
Here is my keyboard I built it in the summer of 2019 and have been using pretty much daily ever since. I bought the case, plate, PCB and stabilizers as a kit for just $36 from aliexpress and the “pudding” keycaps for like 20€. I got the Kailh Box Royal switches from someone at a mechanical keyboards meetup in Helsinki. If I remember correctly I traded them for a bag of Cherry MX blue switches I desoldered from a broken keyboard and 5€. When I ordered the kit there was no mention of any of the PCB’s features and even when I got it I didn’t know exactly what model it was (later it turned out to be an YMDK Bface, a clone of the Winkeyless B.face.) It has a Mini USB port (eww), support for many different 60% layouts, support for LEDs (although with no per-key control besides the capslock key) and can be reprogrammed with the proprietary Windows/Mac only Bootmapper Client (which worked fine in a virtual machine). I’d love to port QMK to it at some point but I haven’t had time to get into it yet.
The stabilizers that came with the kit are really rattly and bad but I didn’t want to wait another month for shipping to get better ones so I went with them. I clipped and band-aid modded them, which helped a bit but they’re still pretty loud and I haven’t gotten around to lubing them.
I’ve been using the keyboard for a year and a half now and I really love typing on it, the Box Royal switches are just perfect for me even though a lot of people seem to dislike them. The case is plastic and hollow though so the keyboard is pretty light and sounds cheap. Or at least it did. I got my hands on an old yoga mat a few days ago that was about to be thrown away so I decided to use it to give my board some extra weight and sound damping. So I cut a keyboard-sized piece of the yoga mat, made some holes in it to put my PCB screws through and stuck it inside. I’m actually suprised by how much of a difference it made. The sound of the keys is much deeper and has less high frequency content. I’ll add sound clips here.
Before adding the yoga mat:
After adding the yoga mat
I recorded the sound clips with a Superlux E205, which isn’t picking up the high frequencies in the first clip really well but the difference is still noticeable.
The stabilizers still sound really annoying, which kinda ruins the sound so I’ll definitely need to look into lubing them next.
After doing my keyboard I also did the same thing to my girlfriend’s Royal Kludge RK987 with some cheapo blue switches but the difference wasn’t that big because, well, blue switches. I also have a Ducky Shine 4 with Cherry MX clears that makes a horrible pinging noise, which I’ll definitely need to do this to. I’ll add sound clips of the Ducky here when I’m done with it.
Update: The pinging noise the Ducky board makes is caused by the springs in the switches so adding foam to the case didn’t get rid of it.