Gents (or Ladies) -- Need help. Have had to jump start my car the past 2 evenings.

* Turn the ignition key and a hear fast clicking coming from the engine compartment.
* All other electricals work fine (radio, headlights, interior lights, warning lights, etc.)
* Car driven only on weekends, but kept on a "Battery Tender". Never driven in rain or if the streets are wet.
* First evening after jump starting, drove the car approx 30-minutes, brought into the garage and hooked up the Battery Tender (did not try to re-start)
* Last night after jump starting, drove for about an hour, brought into the garage and tried to re-start immediately after shutting off. Again, heard fast clicking noise.
* New battery was installed approx 6-months ago.

Plan of action?

Thanks in advance!

Brian