Put a torroid ring on your throttle's servo wire, next to the servo. You're inducing RF noise from your ignition, likely due to setup.

If you ever get into FPV you'll quickly become familiar with RF and the extreme importance of installation, shielded wire, physical separation & torroid rings. I currently have over 25 of them installed in my long range FPV bird w/ absolutely 0 range loss with a 1W VTx blasting nearby!