I recently installed several Seagate 7200.10 320GB HDDs and they were all near silent when in operation (I never consider a HDD to be totally silent when running). In fact all the Seagate HDDs I've installed over the past 3 or 4 years (approx. 30 or so) have been very quiet hard drives. I've had a few Western Digitals that seemed more noisy than normal but the most noisy hard drive I've had was a Maxtor.
If the drive is only making the noise when it's reading or writing I don't think you have to worry about it...but if the clicking noise is constant and you can hear it as soon as you turn on the computer then I think you should be concerned.

Cricket