Wow what weird noise!
 

I was in the 95 diesel today on the highway (95 north in RI) cruising like only she can about 80 mph and I start hearing a loud whirring noise. So I Start shutting things off like the radio, blower and wipers and the noise is still there. I get to my destination and stop the car and pop the hood. Nothing readily apparent but when I turned my lights back on the loud whirring started again even with the car off.

I usually drive with the fogs on as my daytime driving lights so now I know what drives the noise. It seems to come from the front right side of the engine compartment. Can it be alternator related?

ACC auxiliary pump? It might be part of the monovalve in that car.

Sixto
98 320s sedan and wagon
02 C320 wagon

Probably your thermostatically-controlled auxiliary fan.

Yeah, daytime driving lights are not safer, and can sometimes aim into another driver's eyes at the wrong time. Mostly a ploy for the private industry to sell more bulbs.

Problem solved. I saw that my washer reservoir was low so I filled it up and tried the lights again. I saw blue fluid flying out the front end of the car while sitting inside.........the head light washer system is shorting out from the light switch. I pulled the connector off and it stopped. gotta bet a mouse caused this.