tranny noise in 1st and OD around 1600 rpm-any suggestions?
 

I've had this 'noise' in first gear for a while-only happens when I take off from a stop but just decided to troubleshoot it and found it happens between 1300 to 1700 rpm in first and OD gears. is there a common link between OD and 1st? what 'could' be the cause? any suggestions will be appreciated-
thanks,Paul

this is in my 96 suburban K1500 -350ci and 4L60-E. 91000 miles.

it could be the driveshaft, dont rule that out. not always the transmission

update: I drove the truck this morning after it sat all night (~27). The truck (transmission I assume) is making the same sound from 1200 - 2100 in all gears-after it warms up it only in first and overdrive gears. the sound is like a low toned bearing or rushing fluid sound.

any ideas guys?
thanks,-Paul

Process of elimination....

Does the noise show up while in neutral or park at that same RPM? (ruleing out a front pump problem)

Could also be a problem in either differential (pinion and/or carrier bearings), be sure to check the fluid just in case.

it only happens when driving the vehicle-not in park/neutral. I thought about putting the E-brake on and giving it gas to simulate driving the truck but didn't feel standing in front of the truck while doing this was good for my health :-) I'll check the diff's too, I didn't think about the front diff. can you have 'too much' fluid in the front diff? I'm supposed to use 85/90 weight, right?
thanks, _Paul