Matrix 6R abnormality

Hi. I am the original owner of this Matrix 6R. I hadn’t used it for awhile. When I fired it up, everything seemed normal, display is fine. However, it seems that on almost all of the patches, every several notes plays louder, with a slightly different timbre than the rest of the notes in the patch. Usually a harsher sound. There’s a dot that dances across the patch name when it receives midi, and I think that when that dot is in the sixth position (letter), that’s when I hear the distortion. Any ideas? I bought a new battery from Syntaur, as the original is still in there. I haven’t changed it out yet - might that solve this. Thank you.