Allison trans TCC engagement buzzing noise

[jhfarrier2010]

I have a 2004 Silverado with the 8.1L and Allison trans, I have the issue of when the TCC engages I get the buzzing noise coming from the trans. It is especially more common at light throttle, and at times it gets really loud. I read a former thread (which is now closed) on this issue and that there is a technical service bulletin from GM on this issue but no explanation on what causes it or what to do to correct it. This truck is my 6-7 day work truck and it is next to impossible to have it tied up at a shop but the noise is getting irritating. I changed the fluid over to Autran Syn 295 and it shifts better and the buzzing noise isn't as bad but it's still there. Anyone else have this issue or have had it in the past? If so, what was done or what needs to be done to correct it? Thanks, John

[More Power]

Buzzing noise... Could the TC bolts be loose? Is there some other exhaust or vehicle component resting on another part of the engine/trans or driveline that with contact is making noise? Look at ATF cooler lines, fuel lines, exhaust system parts, something..... Jim

[jhfarrier2010]

Thank you for the reply. Seems to me there was a thread I had read at one time about the cooler lines vibrating but had forgottent that I read it. Thanks for bringing it to my attention. I will check it out this weekend. Hopefully this is something simple.