I took my car out for a drive today. A friend of mine was driving behind me. He noticed when I hit the gas hard on the highway that redish brown smoke came out of the exhaust pipes. he said it was lust a little. The engine is newly rebuilt with less then 1,000 miles on it. Any ideas what could have caused it? My exhaust system is kind of old but has no visual rust from the outside.Thinking maybe some rust got blown out the pipes when I hit the gas I hope.