It happened 50+ years ago. Trudi and I were little kids.
With my dad’s permission here’s the email I received.
I was talking to Mom about my memories about Grandma’s house in Laurelton and especially the attic. A “private joke” look went between Mom and Dad and then kind of a blush.
After probing them the story came out. Mom was afraid you could hear everything going on upstairs, downstairs, so Dad went downstairs and Mom bounced around on the bed.
Although Dad heard every movement he told mom he couldn’t hear a thing!