I've got an E350 with a 4R100. Fluid looks good, shifts and drives great but has an erratic ticking sound while in park. Goes away in gear. Using a stethoscope on the top side of the transmission, it is loudest just behind the case vent. Kind of sounds like a marble bouncing around. Anything to worry about?

 

At 45 MPH or above, let off the throttle and then press the OD OFF button. Do you get engine braking? Does the engine speed stay up or return to idle?

 

I do get engine braking. Engine speed stays up.

 

It does it any time it doesn't have a load against it. I'd say it was a cracked flex plate, but it's loudest (with a stethoscope) at the middle of the transmission about an inch behind the vent. Maybe that's just where it resonates most. Who knows.

 

A common problem on the 4R100 is the coast clutch snap ring coming out of the groove. This can cause the noise you're hearing, but if it's come out you won't have engine braking. A cracked flex plate is a possibility.

 

Does it sound like this?

 

Not exactly, but similar. I need to crawl under it and pull the inspection cover and take a listen.

 

Mine used to whine like a bad rear end ring gear or alternator, the shop found my case was cracked when they tore it down for a rebuild at 145,000 miles.