It seems to me that there is something seriously wrong here. First of all, a connected disc should never cause interference in the wii or the television. First thing that comes to mind is that the disc might simply be broken, causing the interference you described. Another possibility is that you incorrectly connected the drive. Normally, it is not possible to directly connect a SATA drive to USB. To do this, an adapter is needed. There exist some cables which include this adapter in the cable. It could be that you are using this. If you are not using an adapter, this is probably your problem. Regardless, even if you have an adapter, I would still recommend a casing, to prevent damage.