I've got an 81 f150 with a c6 auto. I had the transmission rebuilt within the past year and ever since I got it back the transmission makes a buzzing noise in park and neutral. The noise is very noticeable when the truck is cold and only sounds between 900 to around 1750 to 2000 rpms. Once the truck warms up and the transmission warms up, the noise goes away and can only be heard at idle (in park or neutral) up to 1000 rpms. I think it might be a bearing? I never thought anything of it because it was my first rebuilt tranny and I didn't know if that was a "break in" noise or what. Has anyone had this similar issue? It sounds like a literal buzzing noise

 

Check the fluid level. If I remember right you have to drive it to warm it up, and then let it sit in park idling while you pull the dipstick wipe it off, and then put it back in and read the level.

 

I check my fluids every week whether or not the trucks been driven. I double checked my transmission fluid and it's good. It's always done this since I got it rebuilt but went away once the truck warmed up so I never payed much attention to it afterwards. I'm just curious as to what it is. If it's something serious then I'll get it taken care of but if it's not bad then I don't want to spend the money to drop it at a transmission shop

 

Just a crazy thought, but why not take it back to whoever rebuilt it?

 

I've thought about that, only problem is that I don't know who rebuilt it. The local shop in town has done the service and repair for my family's vehicles for years. So naturally I took it to them and they had the transmission sent off and rebuilt. I might just bring it down to them to have them look at it but I got to make sure the truck is cold because that's when the sound is more prominent.

 

I've had a C6 which did the 'buzzing at idle' thing.

I spoke to a trans shop (or researched, I can't remember which) & was told that it wasn't anything to be concerned about.

It was somewhat intermittent, but never worsened or gave any trouble.