1997 Dodge Neon My cars started making this sound when I m

My cars started making this sound when I make left turns above thirty miles an hour in the back passenger side like someone's knocking on my fender. I've had it lowered an inch and a half and I have the trunk mounted strut bar. I thought it might be the bearings but I wasn't sure.

Also. I haven't driven it in about a week and my brother apparently drove it next door and some how or another about a cups worth of what he thinks is kerosene or gas was added. I don't care if it's gas. But I don't know how kerosene will effect my car with my having had it so long with so many miles on it.