2007 Mazda 3 w/ 81k miles has slowly started to develop this knock over the coarse of a few days. Recently changed the oil and it was about 1 qt low. I fear the low oil pressure may have done some damage? Spun bearing maybe? Update on this: Unfortunately I was unable to find a new pulley/clutch/bearing assembly so I ordered a full compressor off of ebay. Then I pulled the pulley and clutch assembly off and swapped it onto the current compressor. That way there was no need to get the system purged, new drier, filled, ect. It's been working great since the swap. I would highly recommend getting a pulley removal tool if you decide to go this route, it makes life easy!
Mazda, engine, knock, noise, problem, clunk, sound, rattle, motor, bearing