That particular PAC alternator-attachment product worries me a bit. At one point when trying to diagnose a ground loop, I tried it, and it did not solve the problem. But more importantly, its connection method is rather "iffy" at best. You have to essentially disconnect your alternator from the car and run it through that thing instead. The problem is that its wires are much thinner (by an order of magnitude) than the alternator wires it's replacing. I did not leave it hooked up for very long, I totally didn't trust it.

Besides, it can only kill noise coming directly from the alternator itself. If you've got a ground loop in the car, you're getting noise from a lot of other places in the electrical system, not just the alternator.