HELP: what is this faint whistle from my gearbox?

[mikeonb4c]

About 3 months ago, I started to notice a very faint high pitched singing/howling sound from my autobox. It was a very pure note, like a harmonic with a slight hooting like quality, that could jump from one pitch to another as the autobox shifted gear. It would only appear at certain speeds and either with light throttle depressions, or on the engine over-run. At first, I couldn't even get passengers to hear it. It has since become a bit more pronounced though it still only happens at certain speeds. It has not got any worse for over 2 months now. It is definitely in the gearbox as it can still be heard faintly when stationary and in D. It goes away if you put the box in N, and also using HOLD on the over-run. The gearbox is working fine and when I checked the ATF fluid a couple of months back it looked and smelled fine and the level seemed fine (though I find it tricky being certain about the level). The ATF was changed a couple of years back and the whole thing cleaned.

I'm baffled as to the cause and wonder how things will progress. Has anyone else come across anything like this with an Autobox. Adrian at Japandirect thinks if trouble brews its best to just fit a replacement off a breaking Bongo (likely cost 500 quid) as opposed to a rebuild (likely cost 1300 quid).

I'd welcome any thoughts, and thanks chums.

[mikexgough]

I'd follow Adrian's advise...... any gearboxes I deal with go off to the specialists.... I take 'em out n whip 'em back in.... You could try another fluid change to see or see if it worsens.... then make your choice

[mikeWalsall]

Any leaking / cracked vacuum pipes acting like a penny whistle ..??

[mikeonb4c]

Thanks guys. Hard to know what to do. Bongo running fine but you wonder if something might suddenly go,and once you notice it the singing sound can be mildly unrelaxing. I'll keep an eye on the fluid and maybe add a bit to see if that changes anything. Can't see any cracked pipes that might contribute but its a point worth checking. I thinkg the sound is too 'pure' though for penny whistle stuff. Its like a harmonic, and I suspect it is connected to the ffluid drive in the autobox (torque converter or suchlike). V frustrating!