anyone experienced noisy phone line for unifi voip phone before?

symptoms: caller of incoming call to my unifi voip cannot hear anything from my side. whereas i can hear them over the phone. also, can hear static noise when i pick up the phone (during dial tone).

wondering how unifi, using digital signals can have static noise, unless something wrong with BTU

i tried rebooting power for both BTU and router then line will be back to normal. so far happened to me twice. still the same after trying with two different TM supplied cordless phone. using alcatel BTU and tplink c5 on Adv50 FTTH.

if i remember correctly, BTU is lifetime warranty by TM?
need to pay service charge if i call them to come change?