Car is having acceleration issues and when it does start to accelerate theres a hard boom

What is your question?

It's an automatic and It only seems to happen at a stop and go. Or if I decelerate back down to 1st or 2nd and start to accelerate again. I'm sitting in park right now and everything sounds fine.

What makes this problem better or worse?

It's an automatic with D4,D3, and 2 it seems to help a little if I start with 2.

How long has your 2000 Honda Civic had this problem?

It just started today