Problem sorted, I found this solution and its working now, a bit fiddly to get the washers in but worth it...
The sound board is connected to the mainboard by a connector and contra-connector, both soldered to their boards.. If you want to do it right, you will have to remove several screws from that bottom corner and left side, under the battery too, so that you can lift up the mainboard's corner (gently!) a bit, and put in back in place firmly. It is located just above the top left side of the battery compartment, when looking at the bottom with the front toward you. A more durable option is to take the bugger apart, and put washers max. 1mm thick under the soundboard to get a better snap-in on those connectors.