tony roberts wrote:
It happened to me with my 196.
Finally discovered the problem. The plane had been in the avionics shop
and while there they had dialed a new frequency into the VOR (don't
remember what it was now). After spending lots of time searching and
testing a friend told me to try switching off all of the avionics - and
the gps came back. Turn on the VOR - lose the GPS! After tuning the VOR
back to a local frequency the problem disappeared.

Worth a try before you start spending money!

Good idea. I should have thought of that. Happens with my handheld, too,
interference from my KX-155 when the NAV side is tuned to certain frequencies. I
think KX-155 is notorious for producing RFI. If the GPS is an IFR approved
installation, they're supposed to check for that as part of the approval, but
who knows. Worth a try.