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I purchased an hyundai terracan turbo 2.9 diesel 2003 last year. I was very impressed with its comfort, power etc. However I soon noticed an unusual noise arising from the engine while at a good speed going downhill decelerating. The greater the speed built up beforehand the louder the noise as it decelerated in speed. I would describe it as a loud humming noise. It sounds as if the engine is labouring too much while decelerating and this is producing the sound. I am worried that this could be causing damage to the engine and also sapping its performance. Any ideas on this would be greatly appreciated !!!

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A different, and much simpler cause, arose on my T-can: A most annouying humm at approx 1800 rpm. Almost drove me crazy. The culprit was the supporting bracket for the gearbox oil dipstick. It runs in a tube, from the gearbox, slightly forward along the engine left side to be accessible near the intake manifold. This tube is supported by brackets, fixing it to the block to avoid vibration breakage but when such a bracket snaps, the bracket itself makes the noise. Replacing the bracket solved it. Easy & Cheap fix :)

Posted on Oct 22, 2009

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I would suspect something else, that is not neccesarily the engine.

If your humming is while decelarating from a fast speed or while going downhill and holding car with engine (compression braking), I will suspect something else like a worn differential. If this is the case, the humming will spread to all the car's body and you will not be able to recreate this humming with a stopped vehicle, no matter how hard you accelerate and decelarete the engine. OTOH, if going downhill on compression braking (vehicle speed held by the engine without using brakes), just press the clutch pedal for a while and check if the humming is still there or if its instantly gone.... If this happens, then for sure the problem is in your rear differential.

Posted on Sep 26, 2009

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This may be something you might check ? the fact that the noise sounds like humming? on rapid decelleration from speed ? as you release throttle from speed downhill the turbo revs drop off and pressured air is reduced into manifold ok ? but the engine speed/rotation is then driven by the drive from the roadwheels/transmission therefor the engine is vacuum caused by induction into manifold is still on increase but due to possible induction hose from turbo to manifold ? this hose may? be collapsing /sucking together thus creating air restriction to engine if this does happen ? then the symptom of labouring and sound of humming you describe may be what is happening? for your info the cause of over rev of engine especially on decelleration from high speed could cause the pistons to catch ip with the valves and bend them? this is a danger to avoid hope this helps?

Posted on Oct 14, 2008

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