Tranny Chatter

Well, I had my tranny replaced last fall, and up until about 2 weeks ago, everything was going good.

When I start my car I get a LOUD shutter from the tranny, but the noise goes away after a couple seconds. I'm not a tech, but it sounds like there is no fluid for a couple seconds. This has been going on for a couple months. But the tranny has been shifting fine, with no problems.

Now, (within the last couple weeks) I have a chatter type noise when the tranny shifts between second and third.....

Any ideas of what it might be, besides another dying tranny?

Thanks.