Birdie after KRX3 installation

[DC1RS]

Today I discovered a strong microphonic birdie at 21.273MHz in main and subreceiver. I'm sure it wasn't there prior the KRX3 installation
So I tried the hints posted here at the list, rerouting of the TMP-Cables and refastening of all the screws.
After a couple of hours try, a screwed up TMP-Cable (thank God there was a spare cable with the KRX3), two extra ground connections from TMP-Cable plugs to the shielding, I succeeded to reduce the birdie to almost inaudibe. But when I installed the top cover again, the birdie in the main receiver got stronger. With removed top cover the birdie is barely audible, but as soon as I get close with the cover it reaches S4. I tried to position the TMP-Cabels again, but no success. Every time I put on the top cover, it came back to S4. Finally i gave up after another 2 hours try.
A quick check of the other bands showed also a S4 birdie in the main receiver at 50.047.8MHz.

Does anyone know about this and maybe got a solution to this?

73 de Roland, DC1RS