Up to the DM
By default, spells do only what they say the do in 5e. Since thaumaturgy does not say anything about granting advantage (though it certainly can allow some sort of sound to occur behind an enemy), by the rules it does not.
However, it is well within the DM's purview to take an individual clever use like you have given here and grant advantage based on it. You will have to talk to them to see if they will accept this kind of ruling however. I also wouldn't expect them to allow it to work every single time you try necessarily.
The DMG does describe cases where granting advantage is worth considering (note not required) with a couple of them being:
Circumstances not related to a creature's inherent capabilities provide it with an edge.
Previous actions (whether taken by the character making the attempt or some other creature) improve the chances of success.
Either one could be applied to the scenario of a distracted enemy, but it would be up to the DM to decide that individually.
It should not be allowed consistently because it impinges on some other features
While the DM is within their right to allow or disallow anything at their table, I suggest not letting this work more than one or two special times. This is because giving advantage is a powerful tool and there are other game features which are made to do this. Allowing things like a cantrip to do it when it is not in their normal ability makes those other features less important. More specifically, granting advantage at range is really good.
There is an action you can take in combat called Help that allows you to give advantage, but only a mastermind rogue can do it at range. This shows you how powerful of a feature it is that it is built into a class. Mage Hand Ledgerdemain, another rogue class feature also allows this.
So, as a DM just watch out when allowing things like this so that you don't cheapen the power of other features.