Misterious noise in a 737
On one of our 734's a very strong noise, quite similar to that of an electric hyd pump, develops under the left overwing emergency exits while in cruise.
It's really strong, and in the troubleshooting we've made we found out it's N1 dependant (it is higher around econ cruise setting), does not varies changing bleed or pack configuration.
What the hell can that be?
Pax are complaining, but our ground engineers don't seem too concerned about that, and I'm afraid they are not going to ground the airplane for a deep troubleshooting.
Engine vibration indications are normal.
A resonating valve in the air ducts maybe?
None else ever experienced the same?
Thanks!