Subject: Possible casues of temporal variation of background radioactive radiation

For several years I have had a Geiger counter running in my house. Registrations
is made by sound, a counter and a dial. Usually I can't hear it, but my guests
do. But if the ticking sound changes I register. Usually the intensity changes
less than +-5% measured over an hour.
But now and then( maybe a few times a year ) I get an increase to 3-5 times
normal intensity. Can stay like that for a few hours or return to normal within
a few minutes. Last time this happen was just a few days ago. It went up to
about 6 times normal for a few minutes.
What might cause those peeks in registrations ?? Showers of cosmic radiation ?
Solar eruptions ? Or a nuclear power station releasing something ?

Any suggestion ?

Regards
John Rehn
Sweden

Re: Possible casues of temporal variation of background radioactive radiation