Transmission noises in 2003 Suburban

[dmcclenahan]

Last week a the transmission in my suburban started making a "coiling/grinding" noise after going into 2nd (speed about 15mph). It doesn't do it all the time and it's only when accelerating. The noise lasts maybe 2-3 seconds. My husband started looking around and found that the transmission fluid was almost empty....I had the oil changed a month ago and supposedly this was checked and everything was at normal levels. We also had the transmission serviced in January. I've noticed a 'clunk' at times when going uphill at low speeds...I think this is a U-joint going out (I've had this happen before in a different GM vehicle and recognize the noise.). However, I'm not sure if a U-joint problem would cause this other clatter. Other symptoms include the "service 4WD" warning that has come on 3 times since we bought it in March 2004 (used). When I've gotten that warning I've turned off the vehicle and turned it back on and it doesn't show up again. A friend has said that this may be a faulty sensor or something. A few months ago this same warning came on plus the indicator lights to the left of the steering that show whether I'm in 2wd, 4wd, etc weren't on (the suburban didn't really know what it was doing I guess). This went away too. I'm calling the mechanic tomorrow (he didn't do the oil change or transmission service but will from now on!).

Any ideas?