Buzzing/whirring/grinding 2004 Hyundai Santa Fe

Can anyone shed some light?? For about a year and a half I have had an “undiagnosable” noise that started as an intermittent metallic buzzing and has evolved into a constant whirring/grinding noise. The tempo of the noise increases when accelerating; occurs at all speeds and at idle. People say they know when I am approaching they can hear my car from about two blocks away. My regular 20 year mechanic checked transmission, replaced timing belt (at 65K; now have about 74K); all idler pulleys; checked alternator; He thinks is is the AC drive pulley on the compressor; Hyundai dealership did not know what it is; laymen have suggested is is a power steering pump, reservoir issue. Power steering fluid level is fine. Otherwise, the performance of the car is fine.

All suggested repairs are in the $1200 range–however, I do not want to spend that kind of money on what someone “thinks” it might be

Engine is 3.5L V6; 2004, about 74+K

Thanks for any insights

Have ALL the heat shields been checked for looseness and cracks?