You're overwriting sound samples with other data before an SPU transfer is about to happen. Solution? Move your stuff somewhere else.

I forgot the other possibility: you're overwriting other sound data that isn't uploaded to the SPU. Basically, if the game is using VAB or whatever other format, it has to keep somewhere in RAM the information useful for playback (offset, loop point, frequency, pitch, etc...) which is managed by the CPU through memory registers. When that information is corrupted you can expect the SPU to simply work randomly and creating all sorts of nasty playback effects thanks to the CPU sending it junk commands.