Toto CST743E noise when flush starts and stops

I installed a CST743E myself and it's much better than the 14 years old toilet it replaces. But it wouldn't be a fun DIY if everything is perfect, would it?

After pushing the flush lever, there is a short sucking sound. The same sound happens again when the flush is done and is a little louder. I'm guess it's the flush valve but it's brand new so it shouldn't be defective. I've also tried to adjust the supply line valve and the water level screw but they didn't make any difference. Is it because the water pressure is too high?

Do anyone else with 743E have similar problem? Thanks,

Kevin

I've not noticed this in my three CST743E's, but I'm not sure what you mean by the sound.

Which fill valve arrangement do you have: Type A or Type B (see the manual, page 4 for a diagram.) If you were able to adjust level easily without removing a white tamper key, then you must have the A which is a screw type adjustment.

Where is the sound coming from: Bowl? Tank? Fill valve? Flush valve?

You could probably determine whether or not it is fill valve related by shutting off the water supply to the toilet, then flushing. If you didn't hear it then that would mean the sound was coming from the fill valve. When you say the water pressure is high, how high?

You mean like this

TOTO Drake 800 grams by Veritech Video