Galaxy pluto (squeal)

[HOUND DOG]

I just bought this pluto off a guy that I know had an occasional transmit squeal. The radio had modulation work in the past to make it TALK LOUD. The only way "I" can tell it squeals is when my watt meter goes up. The squeal is only heard by those I am talking to, not on my end. What I found out is that it will never squeal if the top cover is removed. When you replace the cover, and talk for a while it will start to squeal until the cover is removed again. I use it as a base and just lay a piece of lexan on top to keep the dust out and it works great! Problem is I'd like to put the radio in my truck and it would be nice to put the top back on.
I've tried adjusting mic gain on radio and mic but never solved the problem. It would even "some times" squeal with the stock mic installed and mic gain turned all the way down. I ran a ground wire to the back of the radio case but that didn't help at all. I am thinking about installing some thin insulating board type material that I have, on the underside of the cover to see if that helps.
Can anyone suggest a fix for this pluto?

[HOUND DOG]

well i installed the insulating material under the top cover and screwed it back on. The radio started to squeal almost immediately. I removed one screw at a time from the top cover and it finally stopped squealing when I removed the last (back) screw. Right now the metal cover is set into position on the radio with the insulating material under it but its not screwed on. (Its working ok this way) but starts to squeal when I try to reinstall the screws. If it continues to work without the screws installed, I will put a couple dabs of adhesive on the cover to keep it in place and mount it in my truck. Hows that for a fix?:-)