I didn't know what sex was when I was 10. I knew that sperm from the dad got into the mom to make babies, but I seriously thought they swam through the bed (thus the phrase "sleeping together" and the apparent shock about new pregnancies on movies etc...)
I was probably early teens when I figured it out and then looked it up to see if I was right...yeah, I was a geeky kid.
Anyway, with your dd being blind and having the super hearing, that's all the more reason to be honest with her I think. You don't have to tell her about sex per se if you don't feel she's at that stage (and in her situation I'd think that maybe she's not), BUT you can tell her that mommy and daddy like to spend time together before they go to sleep, and that you like to do things to make each other feel good (if she wants examples you might mention massages and snuggles and kisses etc). I expect she would be able to understand that someone might make contented/happy noises in such a situation. I mean, if you were a screamer it might be different, but if you're a moaner then you can probably get by with that kind of explanation. I do think honesty is the best policy, but it's also ok to only answer as much as they ask (don't offer more info than they are asking for, if that makes sense).
ETA, I agree with the pp's who have commented about knowing the truth being healthy, but too much info is really a taboo thing for most of us (everyone I've ever met). I remember in a college psych class the teacher was explaining about the cultural taboo against thinking about/seeing our parents DTD. Obviously we all know they did it to make us, but we don't want to think about them still doing it, let alone see/hear them. In Freudian terms it's because of the Oedipus/Electra complexes (which I totally don't believe in) but regardless of why it is, it's definitely an ingrained taboo--at least in western society--so yeah, I'd avoid going into too much detail with her unless she specifically asks. Like I said, I'd tell her that it's a loving/good activity, but not discuss details.