The other day I experienced something strange with my 2011 L322 4.4 TDV8. It was during the recent cold snap, I was driving up a steep hill, under load, at low revs. There was a very pronounced loud knocking noise from the engine.

My first thought was “Oh no, that’s my bottom end gone”, but it only seemed to do it from maybe 1,000 rpm to 2,000 rpm. Once I was further up the rev range, it stopped. It was very repeatable on the day, but only happened in those specific circumstances. Slight or steep hill, low revs, under load, low ambient external temperature (the day in question was -3 to -5 deg C, but the car was fully warmed up when it happened).

I’ve been out today in the warmer weather (+7 deg C) and have been unable to recreate the noise. Because I know the car and know exactly what I expect it to sound like, it does sound slightly “off” / gruff to me when accelerating uphill at low revs. The frustrating thing is that if I ask a mechanic to road test and listen to it, it’s not going to be apparent.

Anyone had anything like this before? Anyone got any ideas what it could be?

Thanks