Hi:
Move forward your listening seat.
Mine is a large upholstered sofa bearing on rear wall. There was in my listening room this consistent mid-bass "bump". Radio Shack SLM said +14 dBs around 100 Hz. Tried EQ, port plugging, speaker relocation on floor, new interconnects, lowering speakers close to floor, elevating speakers away from floor, moving speakers away from back wall, side walls, flushing my ears, cutting short my fingernails, eating cayenne pepper and many more things just don't recall.
BUT, when my listening seat was move forward just 5 INCHES !! the mid-bass hump disappeared. Couldn't believe it!!. Pulled back the seat against wall, hump returned. To this day have no explanation for this thing. But listening has been nice since then.
Enjoy!
PS Know no cheaper tweak.