For those of you not familiar with the term resonance harmonics it has to do with vibration and sound.  If you hold a piece of exhaust pipe (or almost any object) and strike it, the tone it produces is at a specific frequency.  If you can put sound into the object at that same frequency the object will begin to vibrate more intensely and produce a louder sound of its own.  This is exactly what is happening on my Galaxie.  At 2000 RPM the frequency f the exhaust and the engine match and the exhaust begins to build up a tone.  The longer I hold at 2000 RPM the louder to tone becomes.  The immediate solution is to increase or decrease my RPMs to mismatch the frequencies and eliminate the tone.  Problem is given my current gearing 2000 RPMs happens at several common speed limits so I hear the tome often and if I am going the speed limit not varying my speed it is constant and builds in intensity.  I am already going to change out my gearing which should make 2000 RPMs something I pass through rather than hold at but if there is something I can also do to the exhaust to help eliminate the problem I would love to here about it.