Knee pain and swimming

Hello fellow swimmers, I'd been letting the swimming slide in favor of running of late--but then came a knee that rebelled, and rather suddenly. Had a perfectly fine run one day followed by mild knee pain, but I blew it off. At 62, if you don't have twinges, you're probably not alive. ;) And I figured, as with other twinges, it would calm down with a little ice. Two days later, I ran but hurt going downhill, so eased off the pace, but otherwise did okay. Then that same day, the knee was throbbing and I was limping. Had some x-rays, went to an orthopedic doctor, who shot some cortisone into the knee. Didn't help. Next step is MRI. But meanwhile, the doctor advised against even swimming b/c of the kicking. So I swam with a pull buoy--but to be honest it's not as good a workout to stick with that. I suppose half a loaf is better than no loaf, but I wonder if I'd really have that much of a problem with kicking. If you've had prior knee problems what was your experience with this? The massage guy I went to said the IT band seemed to be the problem but also very tight quads and hip flexors. One thing I seem to be able to do w/out pain (or a lot less) is walk uphill, so a running coach advised using a treadmill and setting it on an incline--seemed reasonable... eliminate one of the causes of irritation. So today I walked a half hour on the 'mill with the speed going from 3.5 to 4 mph and the incline at 4. That was actually pretty satisfying. I had to back off for a couple minutes in the middle of this b/c the knee began to tighten, but then I was able to resume. This I took to be a good sign, although it's definitely not in running shape yet. Figured I should be getting back to more swimming and doing some open water events--they motivate me to keep up the swimming fitness. But if I build up yards, I want to be able to swim enough of them without a pull buoy to make it count. Thanks for any thoughts on this.