T42G and T48G handset audio problems

[vigmedia]

Hi,

Got 3 x 48G phones about a month and they came with 35.73.0.50 firmware. They had the muffed tunnel like audio on the handset out of the box.
Also got 5 x 22P and 3 x 32G, handset audio is great on those.

Couple days ago upgraded to Firmware Version 35.80.0.20, got it from our distributor, was not on the website yet.
It does seem to make a little difference in sound quality after the firmware upgrade, but the original issue still exists.

Does the 48G need a factory reset after firmware upgrade to apply all the changes?

Can anyone confirm that this audio problem was fixed on any other T4x phones?

Unless there is a resolution for this problem I am sending these phones back.

Thanks,
Csaba