My computer sounds like it is breathing.. Please help.

I installed a new hard drive last week.
Upon my install I took my time air compressing out the dust.

Now.

My computer not very loudly sounds like its taking small breaths.
In Out In Out.
Fairly Quickly.
I have tried to listen to pinpoint the sound but it doesn't seem to be anything in the immediate front.

No fans I have access too are making it.

The new hard drive isnt doing it.

I fear it is the CPU area.

Since that day my computer has been acting very slow.
It has been lagging in processes... files have been failing... the CPU activity monitor is bouncing fairly fast and I dont remembering it acting like that with only Ichat and mail open.
Bouncing up to 30-40% then back to a low number.

I thought maybe I knocked a casing off and a fan was running but I still havent been able to fix it.

Any help?