If it's RF noise, you might try snapping these ferrite cores on the EGT wires, maybe the strobe wires, power feed to the EFIS etc.
https://www.amazon.com/eBoot-Pieces-...ite+core&psc=1
I fixed a wacky fuel pressure/EGT indication when I transmit on certain comm channels with them.
Other thoughts, if able, as a test run the strobes or the EFIS from a separate 12 V battery and see if you can isolate it.
You may also try installing a capacitor on the power feed to the strobes and/or the EFIS.
Good luck, Tim Andres