Years ago I was steered away from 6-axle units, I think the issue (then as now) was 4 axles would give less trouble on smaller radius curves, although it may have had something to do with mechanical noise. Years later, F-units and Geeps of various stripes run great, I have become aware of the noisyness of my U33C(s), PA(s), and FP45(s). The first two I can replace if I have to with Atlas and Proto2000, respectively, but so far no real deals on the Genesis FP45 and I don't know for sure how quiet they are. Anybody? Mike
I have the opposite experience. All of my Athearn BB 4-axles (GP7's and 1 F7A) sound like coffee grinders but run smooth, but I have an SD9 and used to have a pair of SDP40's that all run pretty quiet. I would suggest a good lube job on the gears, but if I remember right the motors make a fair bit of noise by themselves. Personally, I wouldn't replace my BB stuff unless the noise was especially bothersome. My Proto2000 equipment runs reasonably quiet, my Atlas stuff even more so.
Personally, there isn't a lot of difference that I can tell in listening to my 4 axle BB's compared to the 6-axles. Same holds true for the other brands I have too - Proto 1K & 2K, Bachmann. The loudest loco I have is an old Model Power GP-9, nicknamed "the coffee grinder".The quietest loco I have is a Athearn Genesis F7.
run time and lubrication have a lot to do with how quiet most engines are. I find that after some lubrication, my bluebox stuff quiets down considerably, and after a decent run period, it gets quieter.
Might check if the body is loose on teh chassis. The body shell can vibrate causing noise in addition to the motor & gear noise. Some of teh Athearn Blue Box power I have is usually a bit noisier than P2K or Atlas. I havwe a Athearn SD40T-2 that was very noisy. It was teh body vibrating against the chassis. A couple of shims here and there took out teh vibration and the unit now runs much more quietly
I don't find any consistent difference between 4 and 6 axle Athearns. I have a GP7 and and SD40-2 that make about the same noise. An older GP35 is a real growler, while my more recent F7s are almost as quiet as my Atlas units. An SW900 switcher is almost as loud as the GP35.
I have three SD40T-2s that grind but I enjoy the noise. I ran them without the shell and they are very quiet, so it is the shell against the frame, as someone mentioned.
