Weird Engine noise during cold months

During the past few months my 96' 4.3L V6 Sonoma has been making a weird noise on cold starts. It almost sounds like a baseball card in the spokes of a bicycle. This noise will go eventually go away when the engine warms up but it is quite loud when first started. My first thought was the fan was hitting something, but I have no idea what that would be.. Could it be the tension in the belt???

Thanks!

During the past few months my 96' 4.3L V6 Sonoma has been making a weird noise on cold starts. It almost sounds like a baseball card in the spokes of a bicycle. This noise will go eventually go away when the engine warms up but it is quite loud when first started. My first thought was the fan was hitting something, but I have no idea what that would be.. Could it be the tension in the belt???

Thanks!

Is it a clattering noise?

What oil and filter do you use?