At the present time, our company trains only to use less than landing flap (30) for single engine approaches.
One of the surprises in the bulletin I posted was that the flaps extend further at the 30 setting on the 767-300ER and the 767-300 with the "improved" flap system than in earlier models. This higher AOA of the flaps and perhaps its more exposed frontal area is probably what results in the vibration/pulsing.
Since my original post, I have received the revised section of the Boeing 757/767 Flight Crew Training Manual.
"No additional changes to operating procedures are required due to ice accretion on extended trailing-edge flaps. IN ORDER TO MINIMIZE THE IMPACT OF ICE ACCRETION ON AIRPLANE PERFORMANCE AND RIDE QUALITY, AVOID HOLDING WITH TRAILING-EDGE FLAPS EXTENDED WHEN IN ICING CONDITIONS". (emphasis mine)
In our situation, we did not anticipate the extended time we spent at our assigned speed (170K), which required Flaps 5.
Shore Guy