Stinging sensation 1 year after TKR

I had bilateral TKR 1 year ago. Recovery went great and I was cleared to go back to athletic activities...mt. biking, hiking, OrangeTheory Fitness; however, I recently developed a periodic stinging sensation, particularly in my left knee, most often, but not exclusively, when I am climbing or pressing the pace on my mt. bike. It's not terrible and doesn't last, but I am wondering if I am overdoing it? Injured myself?
I am 74 years old.