760 T with 180K miles. Car is great! Have recently (last two days) noticed a faint mid-low frequency oscillating vibration/sound at idle. With mechanics steth, noise appears worse at alternator and at a/c compressor. No noise at block adjacent to crank (which leads me to eliminate main bearing). No noise at P/S pump.... Harmonic balancer?? I will be replacing the timing belt, tensioner, front seals, accessory belts (all three)within a couple of weeks. Should I spring for the H/B pulley as well? Any advice would be appreciated. Thanks in advance.