I noticed a wierd sound the other day and I finally figured it out...it is
my muffler that when the engine runs a little rough at times it makes the
muffler tail pipe come up and hit the van.  Thought I had an engine knock
but it is my muffler just knocking the fiberglass.

So now my ? is do you think the whole engine may be loose somwhere (like
tightening a bolt)because the whole engine seems to shake a little when
this happens.

Also it only happens at turn off of the Van and at certain times during
idleing?