Hello Mike,

I don't have this at all.
I tried to emulate this bee buzzing even by hitting continously full chords and exessive sustain , there's no way I can emulate this.
So it must be your K2600.

Maybe?
There could be some dust on the contacts of your keyboard as the first sounds where you will notice this are the piano sounds.

If you send me a test midi with the bee buzz in it, I could test it and record it for you on my K2600 and send you an mp3 to compare the difference.

Fred