My mom is 91 and drives a 1993 Park Avenue. When we were chatting in the driveway with the car off and the keys in her hand, we noticed some humming from under the hood. It runs for about 10 seconds and then shuts off...tracked it to a part next to windshield washer fluid. The part is kind of silver in front; kinda horseshoe shaped with a black part in back looking like a mini megaphone (sorry for the terrible description). Mom says she sometimes hears it doing this when she walks into the garage. Is this normal??? Any help would be appreciated...when she or I go to a local place, they always seem to "see us coming".