pinging or knocking noise from the engine

Since I have the Blazer '03 (bought it new) I am getting knocking or pinging sound from the engine. Interestingly this is happening during light acceleration or at speeds under 40mph. During idle, under hard acceleration or at speeds above 55mph the engine sounds normal. My city gas milage is fairly low... around 15-16 mph so I do not think this is because of lean mixture. Also tried to use high octane gas, but that does not seem to fix the problem either. Any ideas... anyone knows of a recall that should fix this? The dealer is saying that this is normal for this engine...

I think your dealer is right (if it's light pinging) Using 93 or so octane should've eliminated the noise though. Possibly yours has a lot of carbon that's increasing the compression or perhaps the timing is strayed a bit to far advanced in the light load/midrange.

I'm kind curious since you bought it new , How long has it ben doing it? did it start all the sudden? did you make any changes?

I bought it in Dec 2002, I first noticed the noise about 6 months latter, June-July summer months. Come to think of it, the pinging, knocking sound is more pronounced when it is hot outside and or the engine is warmed up.

That sounds typical of something that is on the threshold of detonation for either mixture or timing. Since the higher octane gas didn't help then it may be a symptom of something else (overheating, timeing,ect.)