Just recently bought an 85 740 Turbo, and noticed that when it goes into the yellow on the turbo guage, turbo engaged, I hear a rather loud hissing. I've tried to read the archieves but have read different opinions. Some say its normal others not. The hissing noise is profound, like the turbo is expelling air or sucking it up profusely. The car appears to have been well taken care of, it has 176K and appears to run well, but is indicative of a tune-up. I can also hear the main pump, which is bothering me as well. Any thoughts on what if anything may be wrong would be greatly appreciated. This board is great.