I think if you take a close look at the whistle on no. 17, you will find it identical to those on the other engines. However, it is what is known as "blown out," steam cut either on the languid plate or the bowl itself, to the point that too much steam is escaping when the lanyard is pulled, causing the whistle to go into overtones and screech. If the engineer pulls gently, the whistle sounds almost like the others. Some folks at the EBT may like that screech, but I remember that Roy Wilburn hated it.
Years ago, no. 15 carried a PRR passenger whistle, which had a different tone than the other whistles. Mr. Wilburn mentioned once or twice putting that whistle on no. 17. Does anybody know what happened to that one?