So I have a 99 Deville 4.6L and it has a very loud humming noise coming from around the passenger side of the engine. Right around the power steering reservoir, from what it sounds like. DTC code is P0507 which shows up twice, one says its pending. Replaced the IAC and cleaned the throttle body. Noise still there. Looked for broken or holes in vacuum lines. Couldn't find anything. Removed the intake manifold and replaced the gasket. Still no change. Also, after replacing the manifold, the engine now misfires. But it hasn't thrown any misfire codes. Can anyone help, please? Thank you.