Use a profiler. You'll find out exactly what those instances are. Note that the application server is never completely idle so it's normal to see some objects being created and destroyed (there are various periodic checks, pollings and so on). But 4.5MB/s is too high.
If you don't have a profiler, download the trial version of YourKit (it's an excellent profiler, by the way). Once you connect to the server, watch the instances and use the delta function to show what objects are created. You may not even need to look at the heap to find out.
The only thing what i found (using yourkit) is the HDScanner, which runs periodically. This HDScanner scans for changed/new files/folder which should be hot-deployed. I could not find anything else which running and allocates memory.
Yeah, 4,5MB/s is too high, is not acceptable. But im stuck here.