Had fault code p227900 come up on my 2015 rs6...says its a air leak ...management light been coming on for about a week...however now when the car has warmed up on tickover its making a high pitch squeal...goes off when you drive it or when the engine is under load comes back on at tickover...has anyone had this before...says it could be between mass air flow meter and the secondary  02 sensors...cheers 

Worn alternator belts make that sort of sound.

Pretty sure it's not a belt problem...the noise is coming from the engine...possibly air sound under pressure escaping...I've ordered a stethoscope to see if that helps to pinpoint it

Check intercooler hoses/intake leaks