low hum noise from 944 engine

[FIA-F1]

this one is tricky. I've got a 90 944S2 cab with 97k miles. It developed a mysterious sound recently but no visible ill effects yet. The sound is audible above the engine noise, and resembles a low pitch hydraulic strain...like an old power steering unit. the tricky part is that it is not consistent. It happens only after the engine warms up. At first i thought it was only in gear, but then it was there in neutral but less so. It comes and goes periodically but appears at least once evertime I drive it. Someone suggested the fan belt may be slightly loose...perhaps. Any suggestion?

[scoober78]

Maybe check tranny/clutch...sometimes they make weird noises just sitting there spinning...fluid flush has always worked for me...

Erik

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Go the distance....

[eligunn]

try to determine where the noise is coming from first is it coming from the engine or tranny? what part of the engine is it coming from, front or back?

[Allldi]

My S2 makes the same hum sound. If we're talking about the same sound, then it definitely is coming from the engine and corresponds with engine speed. My hum has the same characteristics, it only happens when the engine is at operating temperature, and only above 3500 rpms. It doesn't matter what gear I'm in or if I'm in neutral. Also, it doesn't always make the sound. It seems to happen more often during overrun and less often during acceleration. It sounds like a belt to me. I cannot yet tell if it's one of the drive belts or one of the timing belts. My timing and balance shaft belts were replaced about 10000 miles ago and their tension was adjusted 2000 miles after that, so I'm not too worried about it. However, I would like to know for sure what it is.

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Ryan
1991 944S2 coupe