Could be the t/o bearing, or an internal bearing in the trans (happened to me some years ago).
The t/o bearing is a $25 or so part, and if it's noisy now, it will of course fail in time (and get a lot noisier before then).
If it is the trans, you will need a rebuilt unit, but probably not for some time (according to what I have read). Change the trans oil, and drive the car regularly to keep the internals lubed.
The VW that I had with trans noise was allowed to sit for some months, and when used again the trans noise/growl had become an unbearable shriek. Definitly was not the t/o bearing, coz I replaced that w/clutch after the noise appeared.
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