Chas dont assume that because it sounds like its blowing at the downpipes it actually is. I thought my 98 petrol was blowing and bought a complete Toyota one of eBay which was in all intents and purposes brand new. It sounded exactly the same at the front as the one I had removed which on removal was found to have no leak. Maybe what you hear is how they sound.
Hope this is the answer.
Andy (TTG)