[Elecraft] K3S noisy line-out

[W6IPA]

Hi,

I tried looking online, but could not find any reference of what I’m experiencing.
On a new to me K3s assembled from a kit, I have high noise on the line out - which seems to be similar to ground loop noise.
I have no such noise on the headphone jack in the back and in the front or USB Audio. I have tested by using a Zoom H1n line in.
Almost feels like there is a something with this specific connector.
I’ve tried to play with the CONGIF:Lin OUT menu setting - but I always get the same issue. I also tried to disconnect the USB cable with no change.
It’s not critical as I’m using the headphone jack and USB connection without issue.

Anything obvious  I’m missing ?

Thanks

JC/W6IPA.