Well, I just came from the hangar, 9PM and have not made any 
progress. Tried everything suggested. Disconnected the radio/AP 
grounds and run them directly to the battery - same problem
Opened the AP and extra grounded the unit - Nada
Everything that can make noise is making it?
Capacitors as suggested by Chad, did not make any difference.
I'll have to sleep on it. Too tired and frustrated.
Buly

Hi Buly,

 

I've coward away from this thread, mostly because of the potential to get really complicated.  However, I have had some significant alternator noise on Val Com 760 radios in the past, and was told by Val to install a noise choke that Radio Shack sells.  It's part number 270-030A,  which consists of a small transformer, and cap that goes in the power wire that feeds the radio.  This little choke kit was like magic for me, and several others with Val radios (Rich will find one of these on his plane as well). 

 

Now, I don't know what radio you have, but if it's a Val, you need one of these kits.  If not, then it sure won't hurt, and could do some real good.  I'll also warn you that you won't find this part number online.  When I looked for the one for the RV-3, I thought they might have discontinued it, but it was hanging on the shelf at the store, even though it wasn't online. 

 

Good luck,

Rusty (RF noise is not the MRI's friend)