I think I remember reading that the first few generations of digitals could cause interference. All of the old crappy ones should have been sold or replaced by now. I bet you got the dusty boxes on the back of the shelf at the warehouse.
Maybe try calling the manufacturer and discuss it with them. They may be able to tell by the serial number if the units are the old outdated ones.
If that doesnt work call the store you got them from. That issue has to be taken care of if you want cable and dont want cable guys around all the time.....
Might I recommend the old coil ballasts? I was all about the digis for a while. I have bought 4 600W digis, one died a month after I bought it. Now I have stepped up to 1000W ballasts. I get the cheapest one my hydro shop carries. Its like $120, switchable, and a 2 year warranty. They are a little loud and a little hot but its out in my garage so I dont care. I think the old style are more reliable.