What does EMI or RFI sound like?

It's dawned on me that I have some pretty respected line conditioning gear in my system that wasn't cheap to purchase yet I don't know what EMI or RFI 'noise' sounds like . . . My Equi-Tech and Foundation Research line conditioners both claim to remove EMI/RFI but I haven't tinkered around with listening with or without them in the playback chain. In case you're wondering, the Equi-Tech 2Q is a 2,000 watt power transformer weighing 80lbs and provides 'balanced power' while the Foundation Research is a bi-directional filter. I have my CDP pluged into the Foundation Research which is itself plugged into a digital recepticle on the Equi-Tech unit - kind of like 2 sets of EMI/RFI noise supression set up daisy chain like. . .

Any help would be appreciated.