2000 Chevy Blazer knocking sound
 

Hi, I have a 2000 chevy blazer 4.3l with just a hair over 125,000 miles. And recently it has been making this knocking sound on cold starts. And it doesnt always do it.But once it does it makes this knocking/rattling sound and it only does it for maybe 2 seconds then it stops. just had the oil changed maybe 500 miles ago. i put 10w30 in it. Any suggestions? thanks!