Well, you just found out why the previous owner sold it. The timing belt tensioner is failing and is not knocking. I would do that timing belt job, if it is the 2.5L engine not that bad of a job and parts are cheap. Should be able to get it done in a weekend and there is lots of info on the procedure online as the MX6 and Ford Probe have the same engine. The 2.3L engine is a bit different with not as much info but still doable.
2001 Mazda Millenia 2.5L Champagne Silver Mica 190,000 miles
2002 BMW 530iA Sterling/black 95,000 miles
2006 Volvo XC70 Blue 136,000 miles
2001 Mazda Millenia 2.5L Brilliant Black 213,000 miles - SOLD
1993 Mazda 626 2.5L ATX 235,000 miles - SOLD