MacBook Pro :: Monitor Display Not Working Fine / Horizontal Scan Lines And Black Out Occasionally

So I had a recently purchased 17" BTO with the 7200RPM drive that worked great, but with one issue - the display would have horizontal scan lines and black out occasionally. So I called up Apple and eventually managed to get a cross-ship set up(they let me hold on to my current unit, charge my credit card and send me a second brand new 17" unit as a replacement,and then refund me for the second 17" after I send back the defective unit).

Anyway, the replacement unit looks great, but with one issue - there's a very small light dent on the bottom panel(maybe about the size of a dime). I was annoyed but don't think this is worth having to exchange, since I could probably just unscrew the panel and pop it back into place.

However, what really got to me was the fact that my replacement unit was slightly louder than my original - my original is so silent that I can't even tell it's on. However, with my replacement unit, I can hear the hard drive spinning, which is slightly annoying.

Anyway, I proceeded to restore from a time machine backup and test my replacement unit when I noticed that it would occasionally get the hard drive click + beep + freeze issue that many others who have the 7200 RPM drive seem to be facing. It's extremely annoying, and more importantly I miss the complete silence of my older unit.

My question is, while I'm still in possession of both units(which both have the exact same specs, same 7200 RPM drive, etc.), should I simply just open both up and take the silent(good) hard drive from my old unit and put it into my new one?

The click+beep freeze issue is really pissing me off, and my old unit didn't suffer from it - it's just this replacement one(doesn't make any sense).Anyway, would notice if I switched the hard drive? Would I get screwed somehow? Do they keep track of the hard drive serials or something?

I really don't want to go through the pain of sending this back, especially considering that a LOT of people are suffering from this issue, and I don't want to end up with another defective drive. I'm sick and tired of games and just want a computer that WORKS.