New to forum. I drive a 2011 F250 6.7L Has about 15000 miles. Runs great, and pulls our 12000# 5th wheel all over the western US with ease. What a great engine and comfortable truck. About a month ago I noticed an odd screeching or vacuum type noise about 2 seconds after the engine starts. Only lasts a about half second. It will only make this noice on a cold startup even in the warm summer weather. Doesn't make the noise after minimal warmup starting. Had my Ford dealerships diesel tech check it out. He says he was able to replicate the noice by manually activating the waste/dump valve behind the turbo. And claims he got a code on the computer for the same. Replaced the valve, but still the same noise. Since it sounded somewhat like a scweeky belt, they put a new drive belt on. Still has the screaching noise at cold startup. If anyone has encountered this noise with their 6.7l please post. Thanks to all in advance. GHPHOTO