I have been told once that it is not good to whistle after Maghrib because it attracts the Shayateen/bad jinn to you. Are there any hadiths on this?
I seriously doubt if there is a hadith like that. Because whistling in general is considered a bad manner. It is linguistically called: Al-Muka' which is one of pre-Islamic customs and is considered a bad manner. According to some scholars, whistling is not even permissible generally.
Their Salât (prayer) at the House (of Allâh, i.e. the Ka‘bah at Makkah) was nothing but whistling and clapping of hands.
Surah Al-Anfal (8:35)
It doesn't answer your question but just a food for thought.