Funnily enough I have the same problem with 2 x 56s and a 60 with the 60 the worst and have just been battling this one this eve. I've lubricated the axles where the leaflet shows, lubricated the pickups with powerlube, lubricated the carden shafts and tried to drop some powerlube into the motor bearing and bogie gear tower. Both 56s have had the fan drive belt snipped off. Guess what? They all still screech. My models have all been unrun for at least 5 years due layout construction but I've no problems on my 80+ Bachmann, Heljan and vitrains machines but with 1 of 4 60s, 2 of 3 56s having this issue I'm wondering whether there is a difference in grease used by Hornby. My locos have all been stored on shelves in my centrally heated hobby room - wonder if might have been better boxed or stored somewhere cooler?
If you solve the issue please let me know. I've not really stripped parts off the locos to get proper access to gear towers or motor yet but am thinking this could be next...
M