The expression "source of trouble" is spelled with a combination of consonants and vowels that can be challenging for English learners. The IPA phonetic transcription for this phrase is /sɔːrs əv ˈtrʌbl/. Note that the "ou" in "source" is pronounced as a long "o" sound, while the "ou" in "trouble" is pronounced as a short "u" sound. The "ce" in "source" and the "ble" in "trouble" are both pronounced with a voiced "z" sound. Understanding the correct spelling and pronunciation of this phrase can help improve communication and language proficiency.