Replace optical drive with GSA-S10N; discs do not spin?

I purchased a GSA-S10N for my A1181 Macbook C2D (running 10.6). After I placed the drive in, it was hard to insert discs. After the discs inserted, they wouldn't spin, just spit back out. I returned the drive and got a new one. This time, the discs insert smoothly, but still don't spin. It spits the discs out as soon as they are in. I updated the firmware from BP10 to AP12, to no avail. My previous drive was a UJ-857C. The original drive works, it just won't burn DL discs, which is what started me on this quest (it has a problem with the laser when attempting to burn DL discs). So I'm sure that the cable is fine. As rdklinc mentions in the following thread:

Why won't my disc insert into Superdrive?

my new (and old) drive resets itself at startup. I just contacted Computer Geeks, and they sent me a RMA. Before I go through a third drive (which I'm worried may not resolve this issue), I wanted to know if there is anything else I can try. I do have another optical drive cable I will try, but I'm not sure the cable works (from a stuck drive). Any thoughts, suggestions and comments appreciated.