The most common cause of noisy window air conditioner is a vibrating window glass. The compressor of the air conditioner vibrates when it is operational; this in turn causes vibrates things that it touches. Place a hand on the window glass and listen if the noise changes. If so, you have found the root cause and it can easily be fixed by keeping applying insulation tape between glass border and window frame. Applying putty on the window frame will also take care of the problem.
It is also time to consider checking for chips or cracks in the glass. They will surly get bigger by the end of summer. If so, give us a call. We can replace that glass and save the window!