727 noise?

Sounds like the accumulator piston, banging back and forth.Did you remember to reinstall the spring, before the VB went back up?

I think I did, I don't have an extra spring laying around after the install, but I will check that when I drop the pan, thanks! I'll check the sealing rings in the piston as well, I wonder if one leaking would give a similar issue. It definitely seems pressure path related.