I recently retired our Bolt for the reasons of noise and instability mentioned above. It was on an annual plan. One Lifetime Roamio Pro is now at the center of our system. But before I took the Bolt offline for good, I decided to see if I could make it quieter.
The fan had developed a clicking noise early on. I replaced that with a stock model fan, which fixed the clicking noise, but still found the new fan too noisy. I then tried a Noiseblocker BlackSilentFan XS-2, but there's no way around it: that crazy case simply requires a tiny fan and will always be too noisy. I could mod it with a larger fan, but I have better things to do.
Even worse, the noise I thought was a buzzing board component turned out to be a small screw or chunk of solder rolling around under the main board. Apparently it was often vibrating along with the fan motor at times. I haven't bothered to take the board out to see what it is. I'm done.
All previous models were bedroom quiet. Not the Bolt. As I've often said, the Roamio line was the last great series produced by TiVo. If they can't get back to that quality — in hardware, software, guide data, advertising, etc. — well, we're ready here with a Channels DVR system running in parallel and ready to take over anytime.