When you hear a whistle in the dream, then it is a warning. Somebody wants to pay your attention to important things that are happening in your life. Also this may be a sign that you have finished something important in your life and it is time for you to start new period in your life.

Hearing a whistle in a dream represents a warning or something that will focus your attention immediately. Alternatively, you can also mark an end of a period of time, or phase in your life.

…To hear a whistle in your dream, denotes that you will be shocked by some sad intelligence, which will change your plans laid for innocent pleasure. Dreaming that you are whistling, foretells a merry occasion in which you expect to figure largely. This dream for a young woman indicates indiscreet conduct and failure to obtain wishes is foretold….

Hindrances in undertaking already begun. 361.

Personal danger, scandal, and calumny.

you have perceived danger that never will be faced with security.

Dreaming of someone whistling insinuates that people with unknown or hidden interests will try to harm the dreamer. Dreaming of someone whistling may mean that you’ll soon reach the success that you have been waiting for. This same dream in a young woman suggests that her behavior is indiscreet, which won’t allow her to get the things she wants the most. If a whistle appears in our dreams, whether you hear it or not, it is often a symptom of possible disease. If you dream that the whistle is used, it is a sign that you have perceived that there’s danger surrounding you and it won’t be easy to triumph over your enemies.

…To dream about a train suggests that you yearn to do something, but to do so you must travel and there have been problems that have impeded such voyage; however, a train by itself is a symbol of power and strength, which make your goals feasible to achieve. To dream about a lone train riding at high speed suggests that you long for a fast enrichment, and you’re much likely to achieve it. To dream about a half disassembled train and therefore useless suggests that what you desire will be impossible to achieve and that you’ll most likely experience failures. If you listen to the train’s whistle in your dream, it suggests that soon there will be changes in your activities and fortune, perhaps because of the presence of people who were at distance and now they’ll arriving to help you….

…Dreaming of a locomotive running with great speed, denotes a rapid rise in fortune, and foreign travel. If it is disabled, then many vexations will interfere with business affairs, and anticipated journeys will be laid aside through the want of means. To see one completely demolished, signifies great distress and loss of property. To hear one coming, denotes news of a foreign nature. Business will assume changes that will mean success to all classes. To hear it whistle, you will be pleased and surprised at the appearance of a friend who has been absent, or an unexpected offer, which means preferment to you….

…Some time ago I dreamed I left my body, and, after travelling at a great rate through the still night air, arrived at the sphere I designate phantomania. The spot where I settled down was a lonely railway cutting, and I at once remarked on the loud moaning and sighing of the wind through the telegraph wires, and the curious jar, jar, jar of the iron railroad; and the metals which grew less and less like ordinary metals the longer I looked at them, suddenly became imbued with life, and, rising on end, rushed blindly hither and thither and then lay down again. Presently I heard whistle of an approaching train. Nearer, nearer, and nearer it came, and as it whizzed past me all the passengers put their heads out of the windows simultaneously, and burst into peal upon peal of mad, hilarious laughter. There was then a tremendous…

In a dream, whistling represents pagan customs. If one hears a whistle or produces one in a dream, it may indicate an illness, or it could represent a vacant house or a ghost town.

…If you dream of a letter-carrier coming with your letters, you will soon receive news of an unwelcome and an unpleasant character. To hear his whistle, denotes the unexpected arrival of a visitor. If he passes without your mail, disappointment and sadness will befall you. If you give him letters to mail, you will suffer injury through envy or jealousy. To converse with a letter-carrier, you will implicate yourself in some scandalous proceedings….