Last night I was on a Delta MD-88 and before pushback, before the engines were started, there was a loud, highpitched whine that lasted for about three minutes. I was seated right over the wings and I thought that the noise was comming from a box above my head, but I'm not sure.Anybody have any idea what it was?

>Last night I was on a Delta MD-88 and before pushback, before>the engines were started, there was a loud, highpitched whine>that lasted for about three minutes. I was seated right over>the wings and I thought that the noise was comming from a box>above my head, but I'm not sure.>>Anybody have any idea what it was?sounds like your APU was MEL'd and an aircart (ie a huffer) was used to start an engine. they are rather loud (usually a higher pitch whine than an apu).