Now I know the reason for my discomfort. The twin exhaust tips are recoiling (vibrating) noticeably like machine guns. This vibration has gone into the cabin and created a low-tone booming effect that affects my left ear, similar to an 'E" note on my guitar string.
Visually on the exhaust tips - when the aircon is turned off at 650rpm, the recoil lessens. The recoil is most significant when aircon is on at 750rpm. Is it part of running-in?
Unusual step I noticed during Fong Kim's installation, they tied cable ties on all the rubber support dampers holding the exhaust, claiming they can strengthen the supports. Could this be the cause of vibration? Anyone experienced this before?