Thank you for the additional information.
If the licking has been going on this long and is happening almost every night then I suspect tis as now become an obsessive disorder for him much like OCD in humans.
This can happen due to boredom, not enough exercise or could have started during a time of stress and this became his way to self soothe.Click here for additional information
Obsessive licking can also be a sign of pain nausea,or even seizure activity.
The metallic smell can be due to several things the most common being
* Dental disease
* Licking the anal glands resulting in the saliva smelling the same way( It seems you have ruled this out so that is good)
* Liver disease
I would suggest having your vet do a good oral exam looking for tarter build up on the teeth or gingivitis. Full blood work to look at the liver, kidneys and glucose levels would also be a good idea to be sure neither is the cause for the metallic smell.
To help stop the licking I would try to do more exercise before bed to wear him out and see if this helps. This is a breed that really needs to have a job and when they are not exercised enough they can develop obsessive and or destructive behaviors. Another thing you could try is giving a small meal before bed in case he is having some stomach upset and giving a chew toy such as a kong.
If the exercise does not help then you may want to ask your vet about trying prescription medication to reduce anxiety and modify behavior such as prozac and or xanax.
I hope this helps. Please reply back if you have additional questions or concerns and I will be happy to continue.