Welcome to one of the internet's better resources for learning about your car. As fellow former student from RPI, I am sympathetic with your situation - heading into winter with a Diesel in Troy, NY. If you are willing to take instructions from this board you will get all the help you may need.

You have a great car, with the exception of the engine in some instances. It sounds like the rod bending problem has been addressed on your vehicle with the rebuilt engine at 100,000 miles. So you have a vehicle that has likely got more life left in it than a typical vacuum formed piece of plastic built within the last couple of years that goes for an automobile these days.

Unfortunately I dumped my 350SD before I ever had to learn anything about an automatic transmission, and my E300D TurboDiesel has been doing ok in the transmission department with fluid changes every 60,000 miles. However, at some point in the past the automatic controls were operated by vacuum. I am not sure that is the case with the 350SD, but it may. The sound you are hearing may be either an issue with an air intake to manifold issue down stream of the turbo or a massive vacuum leak. Do a search too, as it seems older units do well with a filter and fluid change. Someone here with experience will pipe up - they will likely need a bit more of a description of the problem - and, if you learn to use the search feature, you can do some research on past threads. One nice thing about older cars is you find you are hardly ever the first one to experience a problem now.

If you spend a bit of time tracing out the induction system - intake to air filter to turbo to intake manifold - and looking for either loose or missing hardware holding the tubing together, or missing sensor connections, you may solve your problem, or at least get a handle on it. The later cars have an emissions system implemented that keeps tight tabs on air flow, so a malfunction indication "Check Engine" lights up on the dash if you have a significant leak anywhere. I don't recall such a feature on the 350SD. So you have to check it out yourself. Look at the exhaust gas recirculation connections and valve carefully. Let us know what you find. One key to getting help here is being precise about your descriptions of the problems.

Good luck,

Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)