We have had both Possums and Rats in our roof, and you definately know when Possums are there. They are definately noisier and heavier. I thought there was someone walking through the house when we had a Possum. The Rats move a lot quicker and its a lighter run. When we had some rats, DH put some Ratsak up there and apparently they eat it but go and look for water and don't return if you know what I mean. Good luck with sorting it out.