I have a 25' Safari and had similar noises. Two dealers tried to fix it, but couldn't change the connection method under warranty. The problem is Airstream not following the water pump recommendations - use flexible connections for the pump
. I purchased flex connections at the local hardware store and that eliminated the problem. They run $5 - 10 each.
Here's a link
to what I did (it also shows a small accumulator installed to shorten pump cycling time.