If it were me, I would drive into the local dealer, have the service person come out and look at it and see what they say. It could be some known if rare occurance like a sealant or adhesive that hadn't set up and the sun caused it to drip, who knows what. Won't cost a dime and they might have an easy answer. Having worked with all kinds of electronics for 50+ years, it's unlikely you can just "pop" the front cover off the radio head unit. And if you can, it's likely you'll need a set of spudgers to safely get it off without damaging it or the surround. Love to hear what it turns out to be.