Normal "sounds" for Allison 540?

[RastusM]

Hey all first post here. I purchased an FMC, transit version, one of only about 5 on the road today (440 Dodge engine- pusher configuration). Been busting my xxx on it for a couple weeks and finally today went down and had some tires put on it ... it did fine. But, this Allison 540 is a strange beast to me and I really don't know what it's supposed to sound like. I know they "whine" and it does... seems to shift through the gears just fine up and down. What bothered me a little was the noise it makes in 4th gear, it get's really quiet at some times, I guess mostly when it's loaded (?) and even fairly quiet when it's decelerating but it does make a rather loud whine when it's sort of just loafing, nether loaded or decelerating just sort of when I'm deciding whether I want to speed up or slow down. So really wondering, does this sound vaguely normal? I've checked the fluid best I can... this thing was new 15 years ago and only has about 5K on the trans but some fool installed it with no marks on the dipstick so I'm going to have to try and extrapolate what the heck is actually the right level, tho it's pretty close by the photos I've seen of the stick. Any thought's appreciated, thanks.