An ache would not be part of the resting tremor associated with Parkinson's Disease. Without seeing the tremor it is difficult to comment on the cause or its type. If it is happening frequently try and video tape it for the doctor, also note how long it lasts, and if it can be stopped with movement or activity. Benign muscles twitches can occur in various muscle groups (typically due to overuse), and can look like a "tremor". There is also a condition called restless leg syndrome. This condition is characterized by an uncomfortable sensation in a limb, which is relieved with movement. Other conditions such as thyroid disease and liver dysfunction it seems have been excluded. Good luck.