I believe it happened when the software was updated a few years ago.
Yeah, many existing characters like the apostrophe (’), fractions (½) and many others were prefaced with those unusual characters (Â and others) when the PelletFan software was updated. My guess is that the new software didn’t recognize them in the same way that the old software did.
I think that the only solution is for the OPs to go into their old posts and edit the bogus characters out.
Fractions and such that are included in current posts display okay.