If you hooked the input and output jack grounds together and then connected them to a master ground through a common wire, that's not a star ground. The term "star" is a graphic description of individual connections radiating from a common point. Input and output sharing a ground return is about the worse thing you could do. Try connecting the jacks to your ground point using individual wires for each and see if that clears up your problem.
Star grounding is often undertaken as an overkill measure. There's a widespread lack of understanding of the mechanisms that cause hum and noise, and star grounding is a quick-fix that works much of the time. If you envision your ground paths as a bunch of small resistors in series between your components and an arbitrary "master" ground then it becomes easier to understand. Remember that current flow through a resistance results in a voltage drop which, when it appears in series with your signal, is known as noise. The greater the current flow, the greater the voltage drop and the greater the amplitude of noise voltage that appears in series with the signal.
Returning every single point in a circuit through its own wire to a common ground will usually prevent the problem, but again, it's kind of an extreme approach that could be avoided with careful and knowledgeable layout.
