Its probly Scanning ur Hard Disks for New Media ...... hence the 100% and as its trying to find stuff it wont power down and Hard Disks ... u may want to check the Twonky Settings .......... this would be either u told it can scan on twonky startup or its set to scan every 30 minutes.
After several tests and some weeks experience I guess I found the reason or at least a workaround:
The 100% CPU keeps persistent as long as I have both Twonky and Mediabolic active. After removing the folders for the Thecus/Mediabolic DLNA in the "Media Manager Settings" the CPU is normal again, i.e. gets down on 0% CPU.
So obviously the two DLNA servers affect each other, I have to decide which to use ... very reasonable.