open G string on my TW40 buzzes and gives out a distortion sound. However, if I play it and touch the fishman with a finger through the sound hole...buzz completely goes away and its clear as a bell. Anyone come across this? Remedy??
Sounds like a loose fishman, tighten it or squeeze something under it to stop the buzz.
i had a look inside and it seems one corner is not tightly in contact with the top right at the sound hole. Cant find any screws. Might it be stuck on?
Squeeze a little glue in the gap and prop a stick against the guitar back and the fishman to close the gap.  Don't use enough pressure to strain the back.  Of course clamping the guitar down on a flat surface would help insure that.  Depends how stiff the gap is.  You will have to experiment with the length of the prop to get it just right before using the glue.
Glue alone could be enough to stop the buzz but you don't want the gap to get bigger.
I wouldn't glue it.  Glue is too permanent for something like electronics.  Get some lightly padded neoprene double sided tape.  Pull the control unit off of the soundboard, clean the goo and residue off the guitar and the control unit with a little bit of alcohol and then restick it with the padded double sided tape.  The padding will prevent rattling even if the electronics start to lift away, it is removable if you ever need to service it in the future,  and the good brands of tape will hold for a very long time.  I've been using 3M for stuff like this for 15 years and the stuff I taped down 15 years ago is still holding strong today.
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Thanks all. Im a car bodyworker so have access to quality double sided. I was unsure how the padding would effect the pre amp performance. Ive put it back with double sided anyway. Cured the buzz, sounds beautiful again.