Well, the problem is that the bass is ~5years old and there's no warranty. I have had it to a repair, but they didn't find anything broken(?) I called the store and talked to the guy who sold me this bass in Finland, he didn't have a clue. One thing was sure, no warranty cover in this case.
So, I still have one chance, there's a proff's repair that promised to testrun my bass to see if they could be able to help. So far, no success
Rolle