CO2 injection

I have read a few postings here concerning the use of Aquaclear filters as a way to dissolve 
DIY CO2 into aquarium water.  Not liking the site of a glass bell hanging at the back of my 
aquarium, I thought I would also try this method. I thought of two ways to do this: 1) 
bubble CO2 directly into filter intake tube and 2) bubble CO2 into the small prefilter area 
located above the impeller. Is this how it is normally done? Upon trying the second way I 
noticed this filter making alot of noise due to the impeller "chopping up" the CO2 bubbles. 
I don't know if I am being too picky, but I found this quite annoying. Also, the noise 
seemed to be constant and not just coinciding with the bubbling of CO2 as if the CO2 was 
getting "backed up" into the impeller assembly (I hope this makes sense). To anyone out 
there who has tried this, is this what you've experienced and, if so, what did you do about 
it? Thanks in advance.
Robb D. VanPutte
Dept. of Biology
Texas A&M University