63 Dart Radio issue

I was having issues with my radio cutting out a few minutes after I would turn it on. I could turn it off & back on right away & the same would happen again. So, I had my Dart radio gone through by a friend who does this as favors for friends (He has also done it for a living for over 40 years), cleaned & repaired (found a few small issues) etc. I got it back & reinstalled. If sitting in my garage or driveway, car running or with the ign in acc position, the radio will play all day long. No issues. As soon as I begin to drive around it palys for a few minutes then squeals for a split second then cuts out. Turn it off then back on & repeats the same. Any ideas? Thanks!