There is no noise at the cold start but the noise appears constantly after driving for a few minutes and at idle.

 

It appears that the sound changes (maybe lower noise) when the A/C is turned on, so now I am suspecting if it is caused by A/C compressor clutch?. Can I still drive the car without changing it?

 

If noise stops when compressor clutch engages, that's the issue. If you ignore it the worst case is the pulley comes off and you lose the belt along with the power steering and alternator.

 

If you replace the bearing under the AC compressor clutch before it eats the snout of the compressor you could save $1000.

After the snout gets torn up it is replacing the compressor and having the AC charged. That will easily run up a $1000 bill at a shop.

 

Sounds like the compressor bearings are on the way out