I put an alternator on an 04 f150 5.4. Uneventful, charging ok. Customer comes back next day complaining of a noise that wasn't there before I did my work. I went out with the customer to listen to the noise, it was the "singing" that an alternator makes when charging. I told the customer that it was normal. "Well that aint right, it shouldn't be making that noise". "Sir, thats the noise one makes normally when it charges". "Why didn't the old one make that noise?" "The old one wasnt charging". "Well I want a new one!" I told my SM about it, suggesting he listen to the noise. "I dont need to, just replace the alternator!" So after replacing the alt, SUPRISE! The noise is still there. After several heated exchanges with my SM, HES GETTING A TECH ASSIST! If it wasn't so funny, I'd be offended!