t38G loud buzzing noise in handset

Hello,

I have three Yealink SIP T38G.
Now two with the same Problem.
With a loud buzzing noise in hearer (earphone)

What can i do?
I have changed the hearer (earphone) und changed the Power Adapter.
It is not the Power Adapter and not the earphone.

I want to repair it self.
Witch cap or elko on the T38G Mainboard is broken?
Can someone help me to resolve a Problem?

best regards