Vibration noise when taking off??

[Richh1952]

I just purchased a 99 Sierra V6 regular cab and shortbed, I notice when I take off at low RPM's or low speeds I am hearing a noise like something is vibrating but once I get going and start to speed up the noise goes away! It sounds like something is loose and vibrates on take off so I have crawled under the truck and did not see anything loose but like I say once I get going it stops so anyone else have or had this problem? Any help would be appreciated!!

 

[RayinAlaska]

Not an expert here, but I have had similar problems:

a. When somewhere along the line the muffler or pipes rub against something when you start moving

b. (most common) a loose pebble, gravel, etc. between the catalytic converter and the shield