I have Polk audio M5 surround speakers on short speaker stands. One of these got accidently knocked over by my kid. Now I hear something heavy loose and sliding around inside the casing if I tip the speaker at an angle. I am trying to find any screws or anything to get the casing open to see the problem but there does not seem to be any way it can be opened.

What can I do at this point other than buying a new pair of speakers (not Polk ever again). I will appreciate any suggestions. Thanks in advance.

I would imagine that the drivers(woofer, tweeter,etc.) in the speaker are mounted by screws. You can gain access to the cavity by removing the drivers. Speakers for the most part are completely sealed and the drivers are the last thing to be installed.