Here is an adjustable flow rate valve:
https://armstrongfluidtechnology.com/~/media/documents/installation_maintenance_parts/installation-and-operating-instructions/10-819_astro_express_lf_valve_io.pdf?la=en&display=1
1) I wonder if that would be, or could be adjusted to be quieter.
2) I wonder...
As for parameters 12 & 14, I would at least try to play with them to see if it helps. Personally I would start by setting parameter 12 to 1 minute. Then if that doesn't work, I would keep it at 1 minute, and then set 14 to 1 minute, and I would also try 14 at its max. If setting parameter 12 to...