03 Lightning with 31,000 miles.Billet throttle body,K&N FIPK,Diablo program, biggest lower pulley you can get and billet idler pulleys- all from rpm outlet.Supercharger screams unlike anything I have ever heard. After about 200 miles( with new mods) this noise came about when at idle in gear- moaning- hooting type noise coming from the bellhousing area.(rear main seal) Found if you lift oil dipstick it will go away, or remove oil cap. Replaced PVC valve and checked all vac. lines-hoses for retrictions- none found. Seen Escorts with this type noise and if you removed dipstick o ring, prob solved- On Lightning it blows dipstick up when at full boost ( guage is 1/4 in. past 10) and oil is everywhere!!! ANYBODY HAD OR HAVE THIS PROBLEM!!!!! PS I work at a Ford dealer(28 years in service) and have run it on Oasis ,no TSBs or bullitins.
I had a similar noise that turned out to be a leaky throttle body gasket. Also, check the rubber intake boot where it connects to the throttle body. If you are not carefule, sometimes they fold over on the bottom.
New billet throttle body and gasket and with the set up on the hose on the K&N FIPK its hard to fold that type and not see it esp. where the throttle body is located high where you can see under it, anyways- thanks for your suggestion.I just ordered a vented screw on oil cap- has filter on top like a small K&N cone filter- from Ford Motorsports.NOW if just doen't set a lean code, everything will be alright!!!!