https://bugs.winehq.org/show_bug.cgi?id=37574
--- Comment #13 from Andrew Eikum aeikum@codeweavers.com --- WinXP mode uses the dsound API, while Win7 mode uses mmdevapi directly. This is pretty common for games that use xaudio2.
You're using the unofficial Wine build with the pulseaudio mmdevapi backend. This sounds like an issue with that backend, since the game is talking directly to it in Win7 mode.
I'd be interested to know if this still occurs if you use the winealsa backend with the pulse plugin.
Also, are you using a USB audio device?