Nissan Repair: Lifters rattling?, nissan xterra, lifters

Question
Help.  I just bought a 03 Nissan XTerra V6 (not supercharged).  Test drive of 45 minutes went great.  On the way home for about 10 seconds I heard what sounded like lifters rattling then they stopped.  Today I heard them 3-4 times but never lasting a great amount of time usually 5-10 seconds.  This happens sometimes when accelerating or right before cruising (before 55 mph).   Or could it be bad gas?  I did fill up for the first time this morning with 87 octane. Any ideas?

Answer
Wade,

I would go for the mid grade gas as a minimal to get the pinging down.  That is the noise you are hearing.  If you put in a tank of premium there will not be noise.  I bet you can get away with the mid grade though.  Otherwise, if it continues to ping you could back the timing off a degree or two and it would not knock for sure.