My Svartpilen 401 only makes this sound when you turn the Ignition Key and the TEST-ON-DISPLAY comes up.
So about 2 seconds, than its gone. This seems normal (some kind of testprocedure)
You keep on having this sound, that seems NOT normal for me.
Some people here with a vitpilen701 should post there remarks about this I guess.
Grtz
PDSOUNDS