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Old 02-08-2014, 01:09 AM
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Harmonic noise under load

Hi, My first post so i hope I get it right!!
I have a Jeep Grand Cherokee 2006 CRD with approximately 145,000 km travelled. About 60,000 km of that has been towing a caravan. Have noticed lately that there is a humming noise coming and going like a harmonic around 2200 RPM when under load going up a hill and especially when dropping back to 4th gear under load. As soon as the accelerator pressure is eased off the noise goes away. I have done a complete oil change including engine, front diff, transmission, transfer case and rear diff. Appears to be only normal play in the drive shafts and CV joints. Mounts for engine, transmission etc all seem to be ok. Just can't tell from inside where the noise is coming from. Have searched the threads and have found similar issues but doesn't appear to be any definite answers. Any further suggestions will be greatly appreciated.

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Old 02-08-2014, 01:38 AM
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Re: Harmonic noise under load

does the noise come from the radio, like magnetic interference? that usually is a hum that comes and goes. mine when I had the stock radio would click at certain RPM's. some times it was a hum that picked up with engine speed and would go away when I backed off the gas.
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Old 02-08-2014, 04:59 PM
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Re: Harmonic noise under load

No, I wish it was that simple but I have made sure the radio is off when I try to work out the noise. It is noticeable in 5th gear around 2000 to 2200 RPM but gets quite loud when dropping back to 4th gear (again around 2000 to 2200 RPM) going up a steep hill. It is like a humming noise that goes up and down in loudness every 2 or 3 seconds but when under load (towing a caravan) up a hill and taking the foot off the accelerator the humming noise completely goes away. Put the foot down again and the noise comes back. Once over the hill or no real load the noise is not there. My wife thinks it is from the front to middle of the vehicle. It started about 10,000 km ago and was only just noticeable then but has progressively got louder and more frequent so I presume something is wearing out.
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Old 02-08-2014, 09:44 PM
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Quote:
Originally Posted by Geko View Post
No, I wish it was that simple but I have made sure the radio is off when I try to work out the noise. It is noticeable in 5th gear around 2000 to 2200 RPM but gets quite loud when dropping back to 4th gear (again around 2000 to 2200 RPM) going up a steep hill. It is like a humming noise that goes up and down in loudness every 2 or 3 seconds but when under load (towing a caravan) up a hill and taking the foot off the accelerator the humming noise completely goes away. Put the foot down again and the noise comes back. Once over the hill or no real load the noise is not there. My wife thinks it is from the front to middle of the vehicle. It started about 10,000 km ago and was only just noticeable then but has progressively got louder and more frequent so I presume something is wearing out.
Thats fine. I was just ruling out radio Interference. It could possibility be the swirl motor or transmission. I only say that based on where you say the sound is coming from.
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