accelerator buzzing/vibrating

06 Ford Fusion SEL V6. Have developed one of those quirky problems that I dread even going to the dealership with. At about 2100-2200 RPM, when moving, the accelerator pedal has a buzz feel in it. Like standing on a bee. Only occurs in this RPM range and only when car is in drive. Cannot re-create when in Park or Neutral. Wouldn't be so bad except that this is the RPM the engine holds at 70 MPH, which is where I spend a lot of time. I already know what my dealers service dept. will say. First they won't be able to detect it. Then I will ride with tech and finally yes they will feel. Then, gosh we can't find anything that should be causing that. No TSB out. Closest thing relating is the dash board buzzing that I do not have or notice. Have checked all vapor, vaccuum lines etc. aroung firewall and all are properly secured.
Anyone else notice this symptom, or have any ideas?