You've moved house. The new layout doesn't allow for your favourite speakers to stand 18" from the wall and corners so the bass is a tad boomy as you now have to place them 6" from the wall and 12" from the corners.
You drop the bass control one or two notches and it sounds excellent again with no boomy bass on the tracks where it was worst.
However, the guys on the forum are telling you 'straight' is best and you should instead change cables, change the speakers, change the amp, treat the room acoustics (you've just moved house, you don't have any money), change the music, move house again, do penance at the shrine of the blessed Julian for your sin, stick foam and egg cartons and carpet off-cuts or velcro some cats behind and to the sides of the speakers, get a divorce ... etc. ANYTHING but use the tone control. ("Move away from the knob. Never touch the knob. Go directly to source and do not collect £200 because you are a disgrace to hi-fi!")