1991 300E 4M ... the heater works great when the fan setting is on High, but if the fan is set on Auto or Low the fan very quickly and annoyingly alternates between a whisper and a roar. The period ranges from maybe 30 seconds to a couple of minutes.

Any ideas before I start throwing parts at it? I would ordinarily suspect the push-button box, but it seems odd that the Low setting is acting funny as well as the Auto setting. Makes me wonder if it could be the blower motor?

Matthew
87 560SEL 130K
91 300E 4Matic 100K