Engine noise at low revs under strain

[Stembis]

I have a 2005 Murano with 85,000 miles on the clock. Been running beautifully but recently I have noticed a "rattling or knocking" noise coming from the engine. It is not very loud, and only happens briefly when putting the engine under strain - like pulling away at a traffic light when the car is on a slope. The more gas I give it, the louder the noise.

Also, it only happens when the engine is warm, not when it is cold and it only happens at low revs.

I thought it might be a "pinging" (or pinking) problem that one would get on the older engines when the timing was out, but I didn't think modern engines would do that.

Can anyone suggest where to start looking before taking it to a dealer and spending a fortune.

[njjoe]

Winter gas, perhaps?

Try a tank or two of premium-grade gas and see if the ping goes away.

-njjoe