I have a 2001 F-150 with the 5.4l and a 4R70w transmission. I have noticed a slight vibration while in drive and at idle. It is most noticeable in the brake pedal while sitting at a stop and it seems to get worse if I put the shift lever in L1. Also has a very light buzzing/humming noise that seems to go with it. If I shift into park or neutral the vibration/noise goes away. Any ideas what this could be? It seems to be worse when the engine is warm and the outside temperatures are below 45 degrees.

 

I had a similar problem until I cleaned my throttle body. I used carb. cleaner to cleaned as a routine maintenance and as a result the vibration at idle in gear seem to smooth out significantly. I hope this will help..