I also have had the problem with my MP11DX. I tried all your suggestions as well. My 1st MP11DX didn't start making the noise for several years. It was my favorite calculator as well. The noise was madding. You just had to keep hitting the CE but...
My MP11DX also has a very annoying sound when it goes to sleep. It even makes the noise if I leave it plugged in and turn it off. Only time not making the noise is when it is active or unplugged. Cost too much to just throw out, but very annoying. I ...
