bad running shoes for my knees?

[mosta]

I've never been a regular runner (but when in college 10+ years ago had the basic fitness level of 2 miles/ 12 minutes from other sports). Now I've got the bug. I'm going 4-5 times a week at medium to slow jog pace, 2-3 miles, 2 or so walking breaks--to start. I'm close to 7' tall, weigh 220-225 or so. That's light in a sense (for my height), but also somewhat heavy. (I also tended to I think underpronate a lot (outside of heels wore out fast at an angle)--but my posture's a lot better now and I only feel slightly pigeon toed when I run.)

Question: I like lightweight flats, for the weight, the surface feel, the flat angle, etc. I run almost entirely on pavement. Sometimes I feel some pressure on my knees bordering discomfort, sometimes not discomfort but still I feel it. Is it a mistake to run in these shoes on pavement for me: New Balance rc230, 1 & 1/16th" heel (measuring the rubber outside). I suspect that these may be racing shoes that are supposed to be for occasional use only.