High pitched belt type squeal fixed on ZD30

[Piggymac]

Hey Guys,
I have just recently picked up a 3L GU Patrol. When I looked at the vehicle, i new it had a sqealing noise which I just put down to a noisy drive belt and tensioner. I have been a mechanic for the past 25 years, so you can emagine the language I used after I purchased a new belt tensioner and idler pulley, puting them on and still having a horrible high pitched squeal. I have done alot of reading about this problem and it seems alot of ZD30 owners are at thier wits end with this noise that sounds excactly like a squealing belt. Well after using a peice of hose to my ear, I pinpointed the problem down to the alluminium EGR pipe, ( runs from the EGR valve to the inlet manifold, drectly opposit the fuel filter, on drivers side ). Being alluminium, it is susseptable to warping, due to being mounted to a rather hot EGR valve. It was fine to look at, but when I removed the pipe, (4 bolts ) it had carbon on the surface all the way to the edge, ( this is the surface which is mounted on the EGR Valve, not the inlet manifold ). I put a straight edge on it and it had a definate .5mm warp in the mating surface. There is also a thin metal gasket which mounts between the two surfaces, so when the alluminium surface warps, it creates a small gap and when you give it revs and the EGR Valve opens and exhaust gas that escapes through the gap causes the thin metal gasket vibrate, kind of like the reed in a saxaphone, which causes the high pitched noise you can hear. Ive got a Mate at work with the same vehicle as mine, which was making the same noise and when I checked the EGR pipe, it was warped excactly like mine was.
My fix was to remove the pipe and use a flat file accross it and create a flat surface for the gasket to seal properly. I also used a light smear of Ultra Copper Hi Temp Silicone, which is also sensor safe. Worked like a charm and it made a new vehicle of them both to drive.
Judging by the amount of people having unresolved belt type noises with ZD30 engines, I suspect this may be a common fault.
Another way to diagnose this is to disconnect the electrical plug from the EGR Valve and see if the noise is still present. This prevents the EGR Valve from opening and prevents gas exiting through the warped joint. This will norrow it down to either the EGR Valve itself, or the warped EGR pipie mating surface.
Im not sure if you guys know of this problem, but judging by the forums, it should help someone out there.