You definitely sound like you've got some kind of infection, even if the doctor can't find it...

Here's the thing... Is this piano at a gig, or is it at home? If it's at a gig, mike it and send it to the house system or a small system in front of you that you can't hear. Secondly, tune it! Whether home or gig! Thirdly, that 70db rating... Was that you banging away or playing softer?

Maybe just playing a bit softer (and use the soft pedal) will bring things down a bit, close the lid, etc.. When you get it tuned, talk to the technician about pricking the bass hammers to soften them a bit. That can help with a piano that the hammers' felt has got packed down and hardened.

A heavy blanket over the piano (just leave the keys exposed) is an old studio trick to help isolation. It might help lower the volume.

Hope some of this helps.