2004 S80 - Loud Whistling From Throttle Body

[Shaman]

The vehicle has a loud whistle at the throttle body that reverberates through the throttle body at 1dle and 1500 RPM. Fault codes: P2096 & P2098 detected. What would cause this high-pitched whistle at the AMM and into the throttle body? If I shut off the engine (once it has warmed up) the noise fades away, but reappears upon start-up. It only appears after the engine warms up has been run for a while (approx. 15 minutes). It is definately not a pulley noise. It is coming from the AMM as it joins the throttle body and the high pitched whistling reverberates across the throttle body. DTC codes P2096 & P2098 popped up. (post cat fuel trim system too lean - Bank 1 &2). All vacuum hoses to the throttle body are in good shape and are not leaking. Could this be a plugged catalytic converter applying excessive back-pressure to the intake?
Suggestions?