Alpha One Gen 2 ratcheting sound when in reverse

[watered_down]

I just bought a 2001 Crownline bowrider with an Alpha One stern drive. The boat had 80 hours on it, and after taking it to the lake a couple of times, I noticed a very small oil leak out of the one of the drain holes on the stern drive. After reading on this forum (thanks!), I decided to go ahead and replace the impeller and several of the o-rings in the lower unit. The impeller replacement went smoothly and the leak is now gone. However, when the boat is in reverse, there is now a loud ratcheting noise that occurs when I spin the prop. In forward gear, there is a slight ratcheting noise, which I believe is normal, but in reverse it's quite a bit louder. I don't think it was this bad before I changed the impeller (I didn't check it), but I'm new to boat repair and just want to make sure I don't damage the stern drive. I've pulled the lower unit a couple of times now to try and see if I've done something wrong, but can't see anything that seems out of place. The ratcheting sound comes from the shift shaft, which is no surprise, but I can't figure out why it's so much louder when it's in reverse. Does anyone know what might be going on? I can post a video if that would help. Thanks in advance.