Large Rectangular Craft with lights on its corners. VERY loud, VERY slow.

My dad, my friend, and I were fishing on the beach late at night. For almost an hour, I had noticed a large, dull orb of light across the lake at approximately tree-top level from the perspective of where we were standing. It had the brightness of a street lamp, but just looked strange to me.
To my surprise, the object rose straight up, appeared to pause, then slowly started to move toward us, across the lake. As it approached, we could hear a distant whistling sound, followed by a whirring engine sound, then a faint low rumble.
As it came even closer, we noticed that it was actually a dark rectangle with a  colored light at each corner. I recall seeing at least one red light, and a green light.
It moved VERY slowly, and was not more than 100-150 ft overhead. It was VERY loud, also. There were many houses just behind us, but we didn't see anyone come out to look, which has always baffled us.
My dad had previously been in the Air Force, and he noticed what he called "super-structure" underneath the craft. He described seeing 'girders' underneath the craft, as well. He said that it was moving too slowly to make that much noise.
The craft moved directly over our heads, and disappeared behind some trees.
 As a strange addendum, when we got back to the cottage, we told my mom, and she came outside. We immediately saw the same craft (I assume) in the sky, much higher up, with no sound audible this time.
Even stranger, the very next year, we stayed at a different cottage on the same lake, and I was half-expecting to see the object again. I had a different friend with me this time, and early in the AM of July 4th (Exactly one year later), we were sleeping, and I was awakened by my dog's whining. I heard the same faint whistling and whirring sounds outside, woke everyone up, and I was actually shouting "It's here!!" We went outside to find the same type of craft moving overhead, a bit higher up than the previous year. My parents were flabbergasted, and I was giddy.
We never went back there for vacation again, but I wonder if anyone else has ever seen that object over Ridinger Lake.