Whining sound at 30 and 50 mph

99 Suburban, 5.7 120,000 miles. auto O/D, factory tow package, transmission repaired under warranty at 38,000 miles. At 100,000 miles a trans flush and new fluid. Ever since I can remember there has been a high pitch whine ( almost a ringing sound) that only lasts for a second or two at around 30 and 50 mph when the truck is under moderate acceleration. The whine lasts longer when I am pulling my small 15 ft boat or 5'x8' trailer. I keep the truck in O/D. The sound has not become worse and the truck seems to shift fine. I want to start pulling a larger trailer and do not want to hurt anything. Thank you for your help.

99 Suburban, 5.7 120,000 miles. auto O/D, factory tow package, transmission repaired under warranty at 38,000 miles. At 100,000 miles a trans flush and new fluid. Ever since I can remember there has been a high pitch whine ( almost a ringing sound) that only lasts for a second or two at around 30 and 50 mph when the truck is under moderate acceleration. The whine lasts longer when I am pulling my small 15 ft boat or 5'x8' trailer. I keep the truck in O/D. The sound has not become worse and the truck seems to shift fine. I want to start pulling a larger trailer and do not want to hurt anything. Thank you for your help.

the whining noise is most likely the rear diff...you must change this oil/check condition often when vehicle is used for towing or hauling a heavy load...

REMOVAL of the rear diff cover and cleaning and refilling of the proper fluids is a must...this should be done at least every 30,000mi or whenever the oil looks off color...

the greater the gear teeth are worn the greater the whine..
when you tow/haul do not use OD....3rd gear only....

you also should consider a large trans. cooler to ensure that you have a non eventful trip..