'85 300sd. Have now replaced turbo and went very well. Oil consumption down! Replaced exhaust system and now can hear more clearly that I have apparent whine or moan starting at around 1800 rpm. This was there B4 replacement of turbo and exhaust, but now can hear more. Really noticeable at highway speeds and very pronounced above 2800 rpm.

Ghosts under the hood?

Where do I start? No apparent leaks that I can find.

This is definitely under the hood AND not related to exhaust. From what I hear, it starts around 1800 rpm and increases w/ engine speed. Not in rear end. How do I check for intake leaks?

Since you have replaced the exhaust, it must be something in the intake, perhaps in the air cleaner or its ducting, that is vibrating with the incoming air and producing the sound you're hearing. Perhaps a screw or rivet is missing.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

You hear it at idle? It increases as a function of RPM and not speed? Usually the first suspect of a whine is the rear differential, especially if you only hear it at highway speed.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth