What's that Class 66 "whine" noise?

[ANTONOV 12BP]

This has been a recurring thought that I somehow could not empty from my mind for a while now. But does anyone have a clue as to why some class 66s produce a "whine" sound when on the lowest setting, and why this whining sound is more extensive & audible on some class 66s only, compared to others which do not produce that whine. I've done previous research & googling to see if anyone else questioned what I did, however to no avail I could not find any results. Surely I can't be the only one who has caught onto this fact?

Class 66 with the whine:

(spotter bob/Youtube)

Skip to part 0:56 & 1:17

Class 66 without the whine:

(Trainmania100/Youtube)

Skip to part 1:58

 

[Ayrshire Roy]

The first one sounds like the traction motors making the noise.
In the second one the loco is under no load and sounds like it's just idling so it's freewheeling when it rolls by.

 

[AM9]

The first one sounds like the traction motors making the noise.
In the second one the loco is under no load and sounds like it's just idling so it's freewheeling when it rolls by.

If you are referring to the first one's rising and falling whine that certainly can't be the traction motors themselves as that would mean that the whole train's speed is going up and down as it passes. It is probably the engine speed as it responds to demand from the motors placing a load on the generator. In order to produce more current for the motors, the generator has to be turned faster and the engine needs to overcome a higher resistance to turning its input shaft. Part of the whine may also be the cycling of the turbo impeller although that seems unlikely at such low engine speeds.

 

[Dunfanaghy Rd]

I am open to correction here, but I believe that the turbo only functions as such at higher revs (Notch 6 -8). Below that it is clutched to the crankshaft and works as a Rootes blower. 2-stroke diesels have to have intake air delivered under pressure to function, even at idle.
Pat

 

[Tynwald]

Uncoupling clutch for blower. Driven off the cam at low revs/load. When the exhaust pressure builds up, it is driven off the exhaust turbine.

 

[Ayrshire Roy]

If you are referring to the first one's rising and falling whine that certainly can't be the traction motors themselves as that would mean that the whole train's speed is going up and down as it passes. It is probably the engine speed as it responds to demand from the motors placing a load on the generator. In order to produce more current for the motors, the generator has to be turned faster and the engine needs to overcome a higher resistance to turning its input shaft. Part of the whine may also be the cycling of the turbo impeller although that seems unlikely at such low engine speeds.

The load being put on the traction motors can increase the noise but being notched on and off low down the speed isn't going too increase much.

Edit; what looks like the correct answer is the posts above mine as mine was just a guess.

 

[Mordac]

See this thread https://www.railforums.co.uk/threads/why-do-class-66s-ying.145949/

 

[Mex I can]

From what I hear the loudest whine comes from the driver, after being forced to drive a 66.

 

[ANTONOV 12BP]

I would like to thank everyone here so far, for contributing to my thread & for providing me with their insight regarding my query in mind. Starting this thread has certainly been very beneficial in terms of me obtaining resourceful info as well as for others out there, who are looking to obtain answers that are more or less related to my question.

See this thread https://www.railforums.co.uk/threads/why-do-class-66s-ying.145949/

Thanks! Whilst my question, in particular is not directly associated to the yinging sound. It is related to the whining sound that is most apparent when the 66 is ticking in that specific setting. Interesting read nonetheless.

From what I hear the loudest whine comes from the driver, after being forced to drive a 66.

Had a good giggle at this!