While driving today, I noticed that there is a constant electrical "hum" in my car, even with the radio completely off. I can't tell for sure, but it might still be coming out of the speakers (if that's possible). It's faint, but noticeable even with the windows down while running. I've had cars with a radio interference before and that's sort of what it sounds like.

I had problems with my MSD coil so I swapped it out recently. Again, I'm no positive but I think the noise started around the same time I did the swap, or shortly after. Can the coil cause something like this? If so, is there a way to fix it?