Before I ask the question, let me preface this by saying this has nothing to do with Airbus-bashing (some poor bloke in the general forum meantioned something about engines whining on Airbuses and got chewed out for it!)
Recently flew JFK-LHR and back both times in a VS 340-600. On the flight over, I noticed a sound that would occur approx. every 2 or 3 minutes and would last about 2-3 minutes. Sounded almost like a muffled engine, something like that. I was on the 3rd to last row on the plane. Was it hydraulics, the APU? Any ideas?
PS. Didn't hear this sound on the return, but I was over the wing that time.