I have an ifd550 nav/com which I notice most recently has a comm failure at certain frequencies, I’ve narrowed it down to between 132.2 thru 135.6 will trigger comm failure after about 2 seconds of mic keying. I can repeat this continually when it is failing but sometimes it will allow me to get enough in when talking to center frequencies on around 132.9. At first I thought this could be a connection problem but now that I’ve got it down to a region of frequencies I’m thinking maybe antenna or swr problems. Any ideas how to troubleshoot further? All other frequencies will allow me to transmit fully.