Let me first describe my setup. The PC is a pretty standard one with Win7 x64 Pro and Cubase AI 6. The soundcard is ASUS Xonar U7 with 2xRCA main output, PHONES and MIC jacks. The sound setup is a bit tricky but I hope my explanation will be clear enough. The sound from Xonar's 2xRCA goes to the AUX IN of a mixer (Alto ZMX52). Then, a guitar is connected to one of the mono inputs of the mixer. The MAIN MIX goes to the Yamaha A-S500 integrated amp for playback (I have passive speakers here), and AUX OUT goes to the MIC jack on Xonar U7 for the purposes of recording.
However, there are two problems: 1) When I press Monitor button in Cubase a weird noise can be heard immediately and it stops only after I disable monitoring. 2) The recording works, however, if I record a new track over the previous one, the sound from previous track goes into a new one (so, when you make Track 2, it results in a mixture of Track 1 and new sound which was recorded) which makes recording a real pain. I've read a lot of forums and the only panacea provided there was turning off Stereo Mix in Windows sound settings - however, my Stereo Mix is already turned off and I have never used it before.
So, are there any ideas of what's going on?