[Shotimes] (OT) loud intake

[van Oss]

Sorry for the OT post but once again, I need  a little help from my friends.

My son's '94 Crown Vic with with 4.6L SOHC is intermittently making a loud,
foghorn-like noise in the intake.  We've ruled out the airbox; it seems to
be downstream of that (still makes noise with the airbox lid & filter lifted
off the box bottom).  There is no visible obstruction in the air tube or the
plastic housing that takes air into the throttle body.

Between the MAF and the throttle body, two smaller hoses connect into the
intake.  We figure these are for the vacuum system.  Would a leak somewhere
in the vacuum system be enough to generate a LOUD sound making its way back
out the intake?

Any other ideas or things to test?

VO