I’ve been biking/walking/stairclimbing for about 10 years now (pushing forty).
I noticed early on that my knees make noise. Kinda disgusting noise if you think about it. But they’ve never hurt, and it didn’t seem to be that big a deal.
Barring obvious injury, what can I expect if I keep exercising?
We got the wife an Elliptical for New Years…spent an extra $200 or so to get to the range where I could use it. I’m 6’5" and it’s got a 20 or 22" stride, I forget.
After extended time biking and walking, I find using the elliptical a little makes my left knee stiff. I figure I’ll stop using it if things don’t change soon. If it hurts, stop doing it. 
Bad knees run in my family. My great grandmother and two of my aunts have a condition – and I have no idea what it’s technically called – where the cartilage in your knees deteriorates. My great grandmother walked with two canes and later was confined to a wheelchair because she had no cartilage left in her knees. Otherwise, she was fine. She took a half dose of coumadin every other day and had an inhalor for her asthma, and other than that was in excellent health. She just couldn’t walk on her knees anymore. She wasn’t a candidate for knee replacement surgery, but I don’t remember why. One of my aunts is now in a wheelchair, and the other, in her late forties, is still walking without assistance. When she takes a step you can hear the bones click together. It’s pretty gross. I think she takes glucosamine or something but isn’t currently seeing a doctor about it. Don’t mean to scare ya, but I’d probably get it checked out.
Well, I asked my family doctor years ago and the response was 'yeah, you may use them up at a faster rate, but it’s 100% better than not exercising. I’m just wondering if anyone has any long term experience of getting low impact exercise, noisy joints and either:
no problems
or
Sudden Explosive Decompression leading to the traumatization of the family pet.