A cut & paste from the ATRA (Automatic Transmission Rebuilders of America) website....
Torqueflight
Buzz in reverse, worse cold. This problem cannot always be fixed. The customer is usually worried that something is seriously wrong and that he is going to have a breakdown that will cost him time and money. The way to handle the customer is to tell the plain and simple truth without blaming anyone else: "Sir, I do not know how to fix this noise." (Pause and wait for that to sink in.) "I do not know anybody who knows how to fix it. I assure you that it is oil noise and will not cause any future problem or expense." The key words here are, "I do not know how to fix it." Your customer will appreciate you honesty and probably find it very refreshing.
Now, let's fix the ones that we can and reduce the complaint on the rest:
1977 and later: The primary cause is the same as the C6 problem. Flat-sand the valve body and channel casting. The secondary cause is end clearance on pump gears. (Always flat-sand the 904 pump to fix shudder and vent leak). Swap 727 gears and pumps until you get a close clearance set.
Late 1968 to 1976: Just forget it. If you've got one that just has to get fixed, install later lockup valve body with the lockup disabled. Here is how to disable lockup or make a lockup body work on a non-lockup transmission: The pressure regulator spring retainer bracket angles toward the valve body and retains the switch valve spring. Use a pair of pliers to bend the angle toward the valve body until it collapses (compresses tight) the spring. The prevents the switch valve from opening by holding it inboard.
