I installed my aftermarket HU a few weeks back and all was fine. I then got myself the boosted dual fakra aerial adaptor. Installed it a couple of days ago and noticed it's causing a high pitched noise which can be heard even in AUX mode.
I tried it with just one of the aerials plugged in, removed it from the power. Made sure all the wires weren't close to avoid interference.
If I put the volume on 0 it goes away as it turns the speakers off, put it on a volume like 1 or 2 and it can be heard. It does become silent when there's enough volume for the music to be heard above it.
Without the aerial plugged in, it's fine!
Any one got any ideas?