I have the same error at boot; no sound for me, but sad Mac error shows immediately with 00000005 and address of 00080000. If I pull the memory board out, I can get past this error and boot from the built-in system rom, but System 7 on the hard drive doesn't have enough memory to boot. I've examined the motherboard for any damage and so far cannot find anything... it looks pristine. I cleaned it anyway in case of capacitor leakage, but no difference in behavior. So far I can't find a clue to the cause, but I'll post a follow-up here if I figure it out.