Strange Noise (transmission)

[bluesrefugee]

Hey guys.

 

Just bought an '03 GMC Sierra Z71. 5.3 Vortec, Auto. 93XXX miles.

 

Came across this thread while researching the "clunking" noise coming from the driveshaft. Thought it was a U-joint but then I saw all of the information on the slip yoke clunk. Seems pretty common. Even my mechanic says it's normal for my truck and is very common. So one noise down.

 

The other is not so easy to diagnose. For about one second before the auto transmission upshifts I hear a strange whining noise. Not a gear whine but not a squeal either. This is going to sound crazy, but at first I thought it was my cell phone ringing in my pocket. It only does it for about a second before the 1-2 and 2-3 upshifts. It is more pronounced on the 1-2 shift. Doesn't do it when shifting to overdrive. It is VERY faint (can't even hear it when over 1/2 throttle) but it definitely is there. The thing shifts fine, and the 1-2 shift is nice and firm, but not harsh. Fluid level is OK and fluid looks and smells fine (looks to have been recently changed). Could it be an issue with the clutches? How about the pump? Like I said it is very faint. I didn't even notice while test driving (probably because I was running the dog crap out of it looking for any problems, love that 5.3).

 

Am I just being picky? Any advice would be appreciated.

[mipsco1]

could it be belt squeal as the trans shifts and the rpms change?