I am hearing a noise similar to a siren when I accerate in gear. There is no noise when in neutral, and it increases in pitch as I accerate and then disappears at higher speeds. I don't think it is the brake pad indicators. What else could it be.

rear differential. does it go away when coasting?

rear differential. does it go away when coasting?
yes it does, the sound increases when accerating only. sometimes I can also here a popping or banging noise coming from the rear when I hit the gas. how serious is this problem and how much should a repair cost.

okay here's the cheapest way to fix it. get another complete diff unit from a junkyard with the same axle ratio. usually they cost a couple hundred and take maybe 2 hours for the average tinkerer to swap out. also make sure you're u-joints are in good shape.