About the whistle, I'd make sure the EGR and ARV are in good shape... You can use a soapy water solution to check for leaks.
Mi 300SD is an '83 so I don't know the first thing about ABS, but it does sound like a sensor...
About the heater, my car does exactly the same. I have been told that I'd have to replace the pink vacuum actuators that tend to go bad with years. These are all behind the radio panel and dashboard. Instead of messing with the flap I'd just check the actuators, vacuum system and fix and replace as needed.

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[/SIGPIC]~cirrusman

1983 Mercedes Benz 300SD - Wife calls him "Chitty Chitty Bang Bang"
[SIGPIC]




1983 Toyota Tercel (Tommy, The little Toyota that could)
1965 Ford F100 (Grandma Ford)
2005 Toyota Sienna (Elsa, Wife's ride)


Gone:
1988 Toyota Pickup
2004 Subaru Outback

1987 Cadillac Fleetwood Brougham
1986 Volvo 740 GL Station Wagon - Piece of junk.
1981 Volvo 242 DL 2 Door - Hated to see it go. R.I.P.
1987 Pontiac Fiero GT