why is it that every time i start cycling my knees start hurting?

[goldfishin]

the knee caps always start getting rough. nothing else seems to screw with them like cycling. why is this? i spin most of the time. i would think this shouldn't happen.

[DannoXYZ]

Seat's probably too low and/or too far back. Most common source of knee pains.

[Rowdy]

I had knee pain from my pedals. Not enough float. I switched to Speedplay and the pain went away.