I was diagnosed with PPMS about 15 months ago and, like you, I had my suspicions about the condition for some time before the final confirmation.
My walking has deteriorated at an alarming rate and I do not trust my knees much at the moment, as they can buckle. Mine creak, but not too loudly. I still have some strength in my legs, but not so much on the right side. I take Gabapentin to reduce the neuropathic pain in the area from my right thigh down to the calf.
I have to be careful bending my legs to reach for something on the floor as there is no guarantee that I will get up again, especially as my balance is dreadful. Luckily, my local OT department has fitted many grab rails about the house and provided me with many aids such as a shower seat and two raised toilet seats.
I was not a keen sportsman like you, but I did enjoy cycling and walking. In my case, there is some wear and tear as I also used to do Morris dancing (what an admission), but I feel that it is the MS that is causing the drastic deterioration. I can only walk a few yards now with a stick, and I use a scooter for any longer journeys.
I cannot tell you whether MS can cause further wear and tear in the joints in addition to the myelin degeneration and its effects on synaptic transmission. It might be something you could discuss with your MS nurse rather than your GP, in the first instance. I find my MS nurse very helpful.
Keep going as best you can but do rest when your body tells you to. Pushing yourself can knock you sideways later or on the next day. You probably know all that already.