[markeb01]

It should really be opened up and inspected. The loud howling noise typical to early Chevy transmissions is usually caused by chips or pits in the face of various gears. Over time this will cause additional damage to the mating gears. In a passenger car transmission this was amplified by the use of bronze bushings instead of ball bearings.

If it has a rattling sound, you could have a bad ball bearing that needs replacing or too much clearance from worn bushings. These are very sturdy transmissions, and can continue working for decades making noise with defective parts. But if neglected indefinitely, repairs are far more extensive when the time comes to fix it.