The audio board from the 2009 A1225 is not compatible, one the flat cable connector is wider than on the 2008 and 2007 models. What worked for me was a downgrade of AppleHDA.kext to the El Capitan version (v. 274.12) instead of dosdude’s Legacy Audio Patch, sound is back to normal. Reg. bluetooth, that is fine too with 10.14.4 and dosdude’s patch tool 1.3.
I find the sound problem really annoying in a mac that works quite well as a video streaming client. I found the audio board 820-2364-A of the 2009 imac in the bay . I’ll get back to this thread, if that does the trick. Reg bluetooth I did both fresh install of Mojave and upgrade from High Sierra and re-ran post-install several times - all with experiment character. As soon as I have Mojave bluetooth is gone. I got around that with an ext iogear usb dongle.
I upgraded my imac 2007 with a Penryn T9500 2.6 GHz Core 2 Duo, a Samsung EVO 860 and the BMC943602CS airport card. Under El Capitan everything works great, the old imac seems really fast but under High Sierra and Mojave (dosdude1.com) bluetooth is “not available” and the sound incl. keyboard volume control is messed up. There is a strange echo and artificial click in the overall sound, which is synchronous to the rythm of the music and which sounds like the speakers are broken or their membranes touch something on every beat. This is only on speakers, headphone sound is fine. And yes, I installed all of dosdude’s patches for the 7,1 platform. Any thought, ideas?