Actually it will turn off by itself in 30 seconds (when accessory power gets cut off).
It happened to me once, got quiet for a few weeks, and started acting up more frequently.
I took it in for services and mentioned this issue to the adviser, and he immediately knew the issue.
He even told me that the replaced relays are of different spec. Even the colors are different.
After that it never happens to me again.
So, in short, talk to your dealer. They knew the problem (which is very common).
If cost of repair is low even if it is out of warranty.