Help identifying noise (on 2013) - possibly under the hood

[Yep-Retired]

My 2013 Expy King Ranch EL 4WD has an odd noise that I can't replicate on command. I am hoping someone can shine a light on it for me! My brother, who managed a motor pool for the army said at first he thought it sounded like a cooling fan on the motor. It is loud enough to be heard over the motor... as a low frequency but loud hum. Sometimes it occurs at start up (sometime before putting into gear) even after not being run for a couple of days, so it shouldn't be cooling anything unless there's some kind of thermostat malfunction. When I hear it, I can shut off the motor and the sound continues. If I open the driver's door, it quits. Sometimes it makes the sound when I am driving, sometimes when idling... there doesn't seem to be any consistency. I have an extended warranty through June but I am concerned that if I can't replicate the noise that they'll charge me a diagnosis fee and send me on my way. Any ideas or suggestions are appreciated.

 

[JamaicaJoe]

Do you have an in dash CD player? Turn it off or pull the fuse.

Sent from my SM-T350 using Tapatalk

 

[Yep-Retired]

I do have one. There is no cd in it but when I can get on the road again I will test that. Thank you.

 

[1oldtimer]

How about the rear heater blower motor? Makes me scratch my head until the light bulb turns on (oh yea moment) haha

 

[Yep-Retired]

I don't think it is that because I had this noise on & off for over a year and I rarely turn on rear compartment A/C or heat (no passengers). It really sounds like it is in the engine compartment, maybe up against or near the firewall even. Thanks for replying. I appreciate it.

 

[ManUpOrShutUp]

Without audio, we're all just blindly guessing. That said, what about Ford's Compressor Anti-Slugging Strategy (CASS)? That's a disconcerting sound that many Ford dealer techs aren't even able to identify for some reason, but normal behavior for these trucks.

Compressor Anti-Slugging Strategy (CASS)

Liquid refrigerant may accumulate in the A/C compressor under certain conditions. To alleviate damage to the A/C compressor, Compressor Anti-Slugging Strategy (CASS) is utilized.

CASS is initiated only under specific conditions:

• Ignition is off for more than 8 hours
• Ambient temperature is above -4°C (25°F)
• Battery voltage is above 8.5 volts during engine cranking

When these conditions are present, the PCM will activate the A/C control relay prior to cranking of the engine. The A/C control relay engages the A/C compressor for approximately 4-15 A/C compressor revolutions or a maximum of 2 seconds (depending upon vehicle application), allowing the liquid refrigerant to be pushed from the A/C compressor. CASS is initiated by the PCM regardless of the HVAC system settings.

 

[Yep-Retired]

When our 8" of snow (and the ice expected tonight) clears, I will try to capture a sound file. Thanks for suggesting CASS, I will research it.

 

[Mikezr]

My guess is the factory subwoofer it's the only thing on the truck capable of producing that low frequency and when u open the doors it cuts power to the audio system. it's a bad amplifier or a garbage connection. Try turning the bass down on the radio see what happens

 

[Yep-Retired]

Thanks, that is 2 of you that have referenced the audio system. I had never thought about the relationship of this problem with the fact that the audio turns off with the opening of the door. Sometimes I turn the audio down without turning it off. I will do some experiments when I get a chance.

 

[Yep-Retired]

So, here's a twist. It was 59 degrees today. I drove my Expedition for a while to run errands in the bigger town, 25 miles away. When I got there and stopped at the first traffic light the sound started up. I turned off the radio to hear it better & sound kept going until I took my foot off brake. It happened a couple other times during idle. I parked in my brother's driveway, took key out of ignition & got out... we sat outside and visited for 30 minutes when suddenly the vehicle made the noise on its own. I opened the door to pop hood & sound stopped. He said it was the radiator fans. So I started the vehicle & let it run. The fans never came on and there was no noise. So, is it normal for the fans to kick on 30 minutes after the motor is turned off in what is now 52 degree weather? If so, fine... if not then I need to use my warranty before it expires this summer!