Heavy Truck Gurus-Strange Noise

I drive a Mack triaxle dump occasionally for friends to help them out. I was driving just before Christmas and it started making a howling noise. It would start out fairly faint then build and get louder then fade away. It got progressively louder and more frequent, with the window down it was very loud. With the hood up it seemed to be coming from the area of the alternator. I thought probably an alternator bearing. The owners were going to get it checked out. I was driving it again Monday and Tues and it started again. When I started it from cold yesterday it was quite loud at first but died down as it warmed up. As the day wore on it would do it more and louder. I noticed that it was most noticeable when empty, on level ground, doing a continuous 30 MPH, at 1200-1250 RPMs. It would start low, slowly build to loud enough to be heard probably 200 yards away, then drop off, then come on again in a minute or two. It could be doing it under a load too but being drowned out by all the other noise. They told me that the mechanic took it for a ride but heard nothing and checked bearings but no indications of any problems. Fan comes on maybe one minute in two hours, it is not related. A week ago I developed an air leak that I thought was probably the intercooler plumbing so I checked out all the connections for that before finding the air leak down low on the right side of the motor. The truck has around 150,000 miles and is a Mack 450 HP. Any ideas anyone?

just a thought power steering pump? I had power steering pump on a cat make some funny noises once took a while to figure out.

Pull the intake tube off the turbo and check the shaft for
movement, shouldn't have any if it does that could be your
problem. Had a truck 34 years ago that was doing the same
thing and that was it, new turbo and it was good to go. It's
worth a look.

Spray some WD40 on the accessory bearings one at a time. If it quiets, it, there's the problem.

Is it by chance when the cooling fan or Compressor kicks on and off..?

Ron.

check pressure side of turbo. oily film around hose
where meets pipe loose clamp will make loud whistle
noise ????

(quoted from post at 21:06:49 02/26/14)
Is it by chance when the cooling fan or Compressor kicks on and off..?

Ron.

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The fan comes on just once for about fifteen seconds in a two hour round trip so that is out. The noise is most noticeable during a stretch where no air is being used, so that is out.

what year and model is truck mack never made a 450
hp engine.give me the serial no. i can tell you
what it has.

(quoted from post at 11:15:43 02/27/14) what year and model is truck mack never made a 450
hp engine.give me the serial no. i can tell you
what it has.

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The truck is about ten miles from me. It is probably an '05, and it is a Granite if that helps. It is probably less than 450 as it is significantly lower powered than the truck that I had which had a 475 C-15 Cat.

the cat has more cubic inches an 05 has an e7
engine 727 cubes 460 hp was max. if its a vgt turbo
could be turo noise.

(quoted from post at 22:31:37 02/27/14) the cat has more cubic inches an 05 has an e7
engine 727 cubes 460 hp was max. if its a vgt turbo
could be turo noise.

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By turbo noise You are referring to a turbo problem right? It made normal turbo whistle up until just before Xmas, and still makes normal turbo whistle. But now there is also this much louder noise.