Hello Together

I've recently replaced my Beosystem 5500 with a Beocenter 9500, because the Beomaster 5500 had an awful ground hum, resulting (presumably) from some defective transistors. I did keep the Beovox 3000 speakers though, because I read that they match the Beocenter 9500 rather nicely. At the beginning there was perfect silence, no hum on any of the used sources (Tape 1, CD, Phono, Aux). But now I gradually start to get hum again. I then found out that there are two types of Beovox 3000 and that I own the old ones (1967 - 1971).

Could those speakers be the cause of the problem and could they cause further harm to the Beocenter 9500?

Thanks for helping.