I had a similar problem with my RV-6A. when the control column was pushed towards the panel the compass swang wildly
It didn't matter that if you made that huge input in flight you would be through VNE in a couple of seconds and that if you just kept the control inputs to normal flight range there was no effect on the compass, the engineer insisted that it was cured.
in the end I purchased one of these items and just stroked it up and down the stick a few times and then suddenly "ping" the compass was not affected.
WERA Screwdriver & Tool Magnetiser / Demagnetiser,0300 | eBay
I hope that your problem can be solved as easily.