Intermittent Buzzing Noise after Engine Shut Off

[wallace1]

On an '03 S80 with 47,000 mi there is an intermittent buzzing, after key is off, from under the air cleaner. Started 1 1/2 yrs ago and not again until last week one time. It ran for about 6 minutes after key off. I touched a motor mounted vertically under the air cleaner and it was very hot. No problem with brakes.

Called dealer and he said probably the brake vacuum pump and likely normal but they would have to check when the symptoms were present. Said could be small vacuum leak, another said could be a switch which is internal in pump and would cost $300 to 400 to replace.

Don't want them to just change parts. Anything I can check?

[11110000]

Isn't there a fan under the ECU/TCU box that runs for a while after the car is shut off? I know I've heard that running on my car for maybe 2-3min.

[wallace1]

This has not occurred since my post over a week ago so it is not something that happens normally. If it were a vacuum leak, would not expect it to be intermittent. More likely caused by a switch that sticks on occasionally.

[she said she was 18]

Isn't there a fan under the ECU/TCU box that runs for a while after the car is shut off? I know I've heard that running on my car for maybe 2-3min.

Correct, there is a fan that pulls air from the cabin to climate control the ECU bay. The plenum runs into the Heat/Air. Volvo says that the car will run some systems for up to 4 min after the car is off. Must be one of the.

Temperature Dependant???