Options:
1. If your current setup is cooling really well, wire the Delta fan to a 7v/12v toggle. At 7v it is *much* quieter and provides roughly 75% (or more) of the cooling performance.
2. Get a Sunon 23cfm fan and try it on you FOP38. It'll be much quieter, but may not manage the cooling quite well enough. If not...
3. Get a PEP66 (heatsink only -- no fan) and put the Sunon on it. Will probably do better than the FOP. If still not quite good enough...
4. Put the Delta on the PEP66 and wire it 7v/12v. 7v will be good for most use, but for extra-heavy use times you can chill the TBird with the Delta at 12v. You end up with the Sunon left over...
