When in traffic stopped under the hood makes a loud roaring noise.

What is your question?

This just started. When in traffic and idled under the hood makes a loud roaring noise like a jet getting ready to take off. But once I get back on the gas it goes away. Looked under the hood noticed the water pump pulley would stall and sometime quit. This morning it was 44 and the heat would not stay on unless I was on the gas. If I was stopped the heat would go cold. Once back on the gas it would heat back up. I haven't noticed anything leaking.