the whole things very odd. your friend hearing a growl that you didn't, they could be making it up. when it comes to these things you should rule out anything logical first such as other people, sunlight or the house settling. i was recently reading how certain molds in older homes can effect ones mind and cause them to see/hear things. same with sounds we humans cannot hear, but the pitch can still effect us. [i don't mean to upset you, it's just wise to rule out logical answers before going to the spiritual just in case.] also, what do mean 'mummified cat claw'? was it whole paw or just the claw of an animal? [and if it was just a claw, how was it nailed to a tree? was it pushed into the tree or was their a nail through it?]
anyway, should you find no logical conclusions to these phenomenons, look into a cleansing and protection [it is wise to do a simple one regularly so you don't have to use a great deal of time and energy cleansing and protecting every inch of your home] you can use a variety of methods and/or objects to cleanse your home. vinegar for example is believed to wash away all energy [positive or negative] using a vinegar solution diluted with water [lemon water might help with the smell, plus lemon helps cleansing] to clean the windows and mirrors in your house can keep spirits out [it is also believed mirrors can be used as doorways by spirits. washing it once a month with vinegar water is believed to close the door] you could also use salt water to cleanse your home by sprinkling it around your house [if you have carpets sprinkle some sea salt on them and vacuum it up] personally i use sage smudge, the smoke cleanses your house. [be sure whatever method you use, that you visualize and feel the negative energy being washed away and replaced with positive energy]
for yourself and your friend, you could do a simple salt water bath, or you could have a shower and visualize dark tar like energy being washed off your body and flowing down the drain far away. again focus and energy is key here.
for a protection, you could do a chant, or hang a protection charm or symbol in your house, and wear/carry one on you. this should be strengthened regularly, but it should keep whatever negative energy away.
it would help if you read a few articles or watched a video detailing how its done, but if you know the basics of magick you'll be fine. just remember to ignore anything after you cast, if you stub your toe for example, don't think the cleansing didn't work and theres a curse on your head, you will begin to welcome negative energy into your life and unknowingly curse yourself. [also, as for this 'mummified cat claw' put it in a box of sea salt and bury it off property. the sea salt will nullify any energy]