I really don't know for sure. There are many variables and I'm looking into this myself because I had extremely loud ringing in the ears start near the end of February and it hasn't stopped since. Of course, this is the first time this has happened to me since before my amalgam removal in 2000, after which my ringing went away completely.

I've been searching for a cause and found two possible ones for me:

(1) I live 2 miles down-prevailing-wind of a coal-burning power plant which, after some research, I discovered spews 720 pounds (yes, pounds) of mercury into the air every year.

(2) My ringing began shortly after heavy ChemTrail activity in my area. I also started having terribly achy muscles for several days after discovering that I was standing outside as several ChemTrails descended directly over my property. I've never had achy muscles before in my life except after heavy physical activity.

I'm keeping a log and have discovered that it has eased up considerably in the past several days. I have noticed that, even though there was very heavy ChemTrail activity since February (at least), that the past 9 days have been 100% ChemTrail free. I watch the sky all day from my office window and this is the longest stretch that I've gone without seeing ChemTrails since February.

I'll continue to log and see if I can find any other patterns.