Only complaint was the constant knocking sound in the garage apartment which was annoying enough for one couple to cut their stay with us short by a day. (luxuryretreats.com)
While a faulty O2 sensor can cause a check engine light, it's likely not the source of the engine knocking sound. (yourmechanic.com)
If you hear a hollow knocking sound, the loaf is done. (happyandharried.com)