this is definitly a sample rate mismatch, but it depends on the situation where to correct it.
A mixdown happens at a chosen sample rate. (f.e. 48 khz)
If your windows plays your mp3’s or wavs back (f.e. media player) they normally should check the sample rate of the mp3/wav and match it so the audio is played back correctly. On some conditions (dependend on the OS install) the player doesn’t match to the sample rate and thus you hear the rendered wave/mp3 at a different tone.
F.e. you render a 48 khz wave and play it back at 44.1 khz: this will sound as if it is pitched down.
It is in fact pitched down because the 48 khz is playd back at 44.1.
Check this link for info about the windows audio system and how to set the samplerate there.
Set the same sample rate for your windows audio the same as you do in cubase, and you’re playback will be ok.
kind regards,
R.