Kara, about the filter flow, I never tried extending the intake on the AC 70, because I knew I wanted to maximize the flow (so two filters was a better option for me). When dropping medicine or small food, the flow pattern was pretty evident. I did try it on an AC50 on a 20 gal long tho. The net result was very little noticeable flow, even at full power. Think bernoulli, and the difference in pressure between the tubes and the full tank, and you can imagine how slowly the water moves from one side of the tank to the other. Except for the downward flow from the HOB, there is very little flow from the tank. If the water level is close to the HOB, the tank will look like it is at a standstill.
As for AC filter noise... there are three things I've run into. First, air bubbles in the siphon tube, they can sometimes take a while to purge, even at full flow. You can test for this by filling the tube with water in the tank, then putting it in the filter without loosing water (I know, acrobatics required), and then running the filter. This way you can see if the noise is coming from that. Second thing I've noticed is the lid not fitting securely. I had an AC10 that had a little stub of plastic that made the lid rattle a bit. It wasn't noticeable until you sit in the room with the tank for a while and then the low rumble makes you want to pull your hair out!
The third thing I found making noise was the impeller itself. I don't think there is a real need to lubricate it, but do make sure it is well seated and not touching the base of the impeller. I have had problems with all my AC20s and AC30s, where the impeller gets caught on the base after a few months of use and I have to get my finger in there to unjam it. If this happens, the impeller can make some extra noise. I'm sure there are other things that can make noise with these filters, but hopefully these give you some ideas on troubleshooting the noise!