what can be done to reduce muffler noise when accelerating?

What is your question?

I have a 2003 Eurovan that became a 2004 Rialta. Once I get up to speed, the noise goes away, but when accelerating the muffler is very loud. The muffler was replaced in the last month. I have heard there is a "valve" to keep the muffler from resting on something that may need to be replaced. Any great ideas?

What makes this problem better or worse?

accelerating

How long has your 2003 Volkswagen EuroVan had this problem?

since I got it a week ago