Relationship between HD cache and burst rate?

[bonez318ti]

I recieved my refurbished (via: IBM Certified Used) yesterday. I've been browsing this site and decided to dl HD Tune to see if this HD problem affected me. (I've been hearing clicking when my computer should have been idle)

Well, lo and behold, HDTune says that my HD has 0 buffer. The clicking noise is intermitten, sometimes it is like 1 or 2 per second, sometimes it goes for a while before clicking.. and sometimes the clicking is really faint and sometimes (only 2x) it was very loud.

I ran the benchmarking test, with everything off (antiviruses, etc) I get:
Access Time: ~20
Burst Rate: ~70 Mb/s

Im not very technically inclined, but some people have mentioned that 0 cache should not show very high burst rates, so there must be cache.. and HDTune is misreading the cache number?

Does that sound right? Anyone know the relationship between cache and burst rate?

By the way, my hd is HTC42040G9AT00, its the 40 gig version.

Thanks