Ok folks, this one is weird.

05 express 3500 box truck. I was checking my tranny dipstick with the engine running, and was noticing a high pitched whistle all of a sudden, like a leaking vacuum hose. The dipstick was pulled out. Upon listening more closely, the whistle was coming from the dipstick tube itself. No transmission fluid spurting out or anything. I covered the tube opening with my thumb, but couldn't feel air sucking or blowing. The whistle stopped too. When I uncovered the tube opening, the whistle came back and at much higher pitch, then shifted pitch down, then again resolving to the original pitch of the whistle (as if there was pressure being built up when I plugged the opening with my thumb, then released).

It sounded like a flute....

Obviously there's something pressure wise happening here, but I've always heard the bad signs when there's air coming out of the tube, mainly the oil.

Again I couldn't feel air, and fluid wasn't spraying out.

Any thoughts on this? Vacuum leak on the other end maybe? No codes or leaking tranny fluid....

 

Resurrection with about the same problem. On start, the transmission oil dipstick pops out of the tube. Another symptom for mine is taking the stick out and putting back in, it doesn't want to for about the last 8 inches. Today I coaxed it down to about an inch or so, but still has tension when locking into the tube.

Mine is a 2005 express 2500, extended.
First big question, what might be the problem? Low/high fluid?

Second, how do I find the correct length the dipstick should be? PO might have replaced with the wrong dipstick. I know I can drop the pan, would like to get this quicker.

 

Not an expert on auto transmissions, but I know they all have a vent, and you don't want any gear-box pressures, as that could blow out a seal, auto or stick, but sticks run cooler as no torque converter. Might not be a bad idea to allow the pressure out of the dipstick until you can find you why you have that pressure in the transmission.

 

"Second, how do I find the correct length the dipstick should be?"

No idea on tracking the specified length.
It may vary based on years and engine type.
2003 Express 3500; LQ4 6.0 L V8: from base of plastic handle to end of dip stick = 64 1/2"

I also have found the transmission dip stick pull handle popped off the tube.
It has happened erratically and not for a long time now. No cause was isolated. Tension on the metal dip stick was suspected.
There may be a "magic" word the designers have withheld.