I have noticed a small spark when inserting a cord plug into an electrical outlet in the old house we have just purchased. All of the electrical appliances seem yto work OK and we don't get this small spark every time. There are still a few circuits of the old "knob and tube" in the house also. Could this be causing the trouble? Could some one explain to me what "cross or back feeding a circuit is"?
Thanks

Could also be just because the devise you are plugging in is turned on. For example if an iron is on and plugged in it will probably spark when plugged in.

I agree with MA. If the device you are plugging in is "OFF" and you still get a spark, I would consider replacing the device. I'm surprised your homeowners insurance didn't make you remove all the knob and tube... this seems to happening more frequently.