so, driving my "new" 1990 245 today, i heard a very wierd sound, something like a deisel klunking, at first methought that it came from surrounding traffic... then, alas! it was my car! uh-oh cell phone was with my wife... now what? it was persistent... sounding like a bad muffler. after several stops, look-unders, i was baffled... after 30+yrs of volvoness, i thought i knew it all! weirdest was when my distributor cap cracked and ignited the center rubber mount from a way-overheated orange-glowing catalytic converter... nah! i wasn't gonna get suckered again...
answer: the rear door speaker was doing its unpredictable crackling sound... adjust the fm radio dial... stoopid! sometimes you just cannot identify a problem... do less. learn!