Well, just thinking about your setup really quickly, the SRT should be acting as a conventional Mixer only based on what you are saying. Meaning If you are using the A10, then you must be using the RCA inputs right? And not connecting the 900 SRT to your laptop at all via USB.
If this is the case, I can't see why the SRT would be doing this with the combination of the things you are using. unless it does it for any audio source going in that route.
If you have access to the 900SRT, I have a couple of suggestions:
-Try installing the DJM 900 SRT drivers. If you have it, reinstall it.
-Try using the SRT as your sound card to eliminate the A10 from the equation. (I have used the SRT once before with Traktor and I had no issues).
If you experience the same issue, then you know it's more than likely the mixer. If you do not, then I would guess that the A10 is causing this.
Have you also tried using a different USB cable from your laptop to the A10? Try to use one with ferrite cores on it. You should be able to get them for under $20.