Red sphere or light traveling low and fast but silent in Spring City PA

Driving home and close to my house, I saw a red sphere or light traveling at about 2500 feet.  It caught my eye because it seemed faster than a helicopter or small plane.  Definitely was not a commercial airliner.  It was moving NNE and had no anti collision lights or any other lights around it.  It was at a 40 to 50 degree angle from me and made no sound which I thought I would hear compared to my lifetime experience.  I always watch the sky and am very interested in all aircraft.  The only thing I can speculate is that it was a low flying private jet that did not have any lights on except one red light.  Still it was silent.