Hello,

My 1997 C280 with 87k miles and the 722.6 tranny has started exhibiting a strange noise. It makes a very high pitched whinning noise that only appears at 52-54 mph. It started about a week ago. It sounds like it is coming from the engine/tranny area, but it does this independent of engine rpm. i.e. I change change gears and thus revs and the noise is still there. So the noise does not depend on engine rpm, only road speed.

Also, it only does this when the transmission is operating and relatively cool temps but after it has warmed up a bit, around 100-130 degrees F or so. So, my first inclination is to believe that it is somehow a tranny related issue, but I really don't know. If I sit in traffic for a while so the tranny warms up a bit more, and then try to demonstrate the noise again, the it disappears completely.

The noise sounds somewhat like the noise in this post that Donnie said was the cold oil rushig through the oil pump in the engine. However, on my car, the noise is much higher pitched and does not increase in frequency as the engine revs higher. Also, engine coolant and oil are at operating temp when this noise occurs.
http://www.peachparts.com/shopforum/showthread.php?threadid=35065&highlight=oil+pump

I understand the extreme difficulties in diagnosing the description of a sound over the internet, but I thought maybe some else may have encountered this specific problem and I might get lucky. Everything works perfectly, but the car did not do this a week ago, it is not normal and I just want to make sure that I do not have any major problem in the future because i neglected some warning signs.

Thank you,
Ali Al-Chalabi

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record