A good friend spotted this sign in a restroom at Disney World and snapped a photo to share with me. He commented that it amazed him how much the deletion of one letter from the beginning of a word can totally change the pronunciation of the word. I think the oddity of this example comes from the fact that when a string of consonants starts a word and one of the consonants is dropped the resulting word usually still rhymes (ex. "bloomed"..."loomed", "crusted"..."rusted", "strap"..."trap"..."rap", and so on).
That is not the case here, and part of the reason is that we are talking about consonant sounds, not letters. The word "changing" may start with two consonants in alphabetical spelling, however, phonetically, the letters "c" and "h" combine to form one sound - /ʧ/(aka /č/).
So, phonetically, we have "hanging" /hæŋəŋ/ compared to "changing" /ʧenʤəŋ/.
By adding the letter "c" to the "h" in the word "hanging", the word initial sound changes from a fricative to an affricate. Because sounds like to hang out with other sounds with whom they share commonalities, it is not surprising to see the affricate /ʤ/ in the word "changing". It also does not surprise me that the /æ/, which is a lax vowel, becomes /e/ (a tense vowel) in "changing" because if consonants were classified by tenseness, I would think that affricates are more tense than fricatives.