About a couple of months ago, I had new Bridgestone Potenza RE730 tires mounted and balanced on my stock TT rims. However, I notice the the tire on the rear driver side loses about 5psi per week. All the other tires say about the same. I leave it at 36psi on all fours, but when I check that one tire one week later, I get 30psi. What should I do? Is this normal? If not, should I go back to the tire mounting place and try to get them to mount it again? Any advice would be helpful.