They often resolve with rest, anti-inflamms or may require a steroid injection and some physio treatment. Your very sensible getting it seen to before it causes issues with your running because it will be easier to sort out now.
If it's behind your knee it is more likely to be a tendon either one of your hamstrings or adductors. If you are particularly tight in these muscles the tendons can click around a bit and then as you warm up and the muscles lengthen out a bit it will settle. Try some dynamic stretches before you run and then static stretches after a run.
There is good evidence out there to show that medical grade compression socks can aid in recovery and the theory applies to performance also. The graduated compression helps with your venous return (pump the used blood back to your heart) and this will make your calves feel much better, rather than deoxygenated blood pooling in the lower leg.
Calf guards are ok, but they tend to only have 1 strength of compression, you get more benefit from graduated compression which encourages the blood to pump back up the leg both while running and also for recovery. There are some great products on the market.