Precursor: If I play Warlords II deluxe (W2D) on my 486, it works as intended. No hanging notes, no crackling noises. No matter which patch version of 2.2.4 and 2.2.6

If I take the W2D folder to my modern machine, use Dosbox 0.74-3 and select any Synthesizer (like General Midi or Roland Sound Canvas), the test melody will play and sound right. But at the end, one or more notes keep hanging. They only stop playing whe I close Dosbox. If I select OPL music, the sound works. The problem also exists in the actual game.
This is the main problem I would like to solve. I would be glad to get any solutions to that.

Irony: I thought I just save me the trouble and spend 3€ for the game on GOG. Same problem with the GOG version PLUS it makes crackling noises when the mouse is moved over pushable buttons. Any solution to that? I am experiencing this on several computers, so I suspect it is a more general problem.

Thanks for any help.

(Edit: After changing the settings in the GOG config files to the same defaults I was using, the crackling vanished. Still, the midi problem remains.)