you have to distinguish between transformer hummmmm and ground loop hummm. Ground loop usually can be delt with either a cheater, 2 prong pc (Vans Evers comes to mind, they have a grounding wire so it can go either way) or a ground isolation transformer for your cable TV line (vbery common source). Transformer hummm is a physical thing actually harder to deal with. Sometimes it results from excessive dc leakage and there are products to handle that (one by auidoprism I think). Sometimes its poor design or construction of the transformer and then there may be no hope.
