Every now and then, after a rainy day or during a cold day like today, when I turn on my Blazer, it makes a rattling noise. When I step on the gas, the noise speeds up and gets a little louder, but eventually goes away after a it's warmed up. Any help? I can post a video if that'd help, just want no more troubles with my baby.

 

where is this noise coming from, You are very vague describing it.
A video would also help.

 

Thats funny mnie has been doing this since last winter. First started on a 5- zero morning. Goes away within a few minutes

 

You think there's anything wrong with it? Something that I should be worried about ASAP?

 

Sorry, it sounds like it's coming from under the hood, in front of the radiator fan. I think it's called a timing belt? I'll try to get a video soon.

 

Could be a bad pulley bearing. its a serpentine belts also

 

I have a 2000 Lt Blazer 4x4 with 106K miles on it 4.3 eng. I bought the blazer in 2002 and still have it. It has made that noise every since I bought it and I have change everything out on the front on the motor. Still there...A mech friend of mind put a tool against one of the valve covers and said it was a lifter or lifters...I still drive it noise an d all...

 

Not sure if it's the cause of your engine noise, but, piston slap is very common on 4.3L & 5.3L GM engines. The noise generally ocurrs when engine coolant and ambient temps are both ~40F or colder. It can last from a few seconds, to almost a minute. It is most noticeable in neutral, while increasing the RPM, (usually slowly is enough to notice). If you let off the throttle, the noise is almost undetectable, and you may or may not notice it at idle. Piston slap is caused by a lack of lubrication to the lower cylinder walls on cold start up. When the piston is at BDC, (bottom dead center) the tips of the piston skirts extend below the lower end of the cylinder wall. As the piston begins moving upward, the skirts contact the cylinder wall as the piston centers itself in the cylinder bore. Some engines have this problem right from the start, others develop the noise as the engine wears, and some never do it at all. The use of a good quality, fully synthetic motor oil, changed regularly ~4K miles, will usually keep the wear in check, or quiet it down completely. Don't expect immediate results though. Depending on how severe the piston slap is, I've seen them last in excess of 200K miles rattling like that. The "fix" is rebuild it and hope for the best.