D lacking power, uneven volume

Hello

My bass is suffering from unevenness. Especially the D notes seem to lack some fundamental bass power. Then again the C notes are very loud and boomy. The problem has always been there but now it has really started to annoy me. Acoustically it is not as clear, but amplification (with a Revolution solo 2) exaggerates the problem. There is also a bad wolf tone on the Bb.

The bass is carved, made in Czechoslovakia, similar to the ones now sold as Strunals. I would be grateful for any ideas or experiences how to fix this.

Regards
Babajo