Really says it all. What type of instruments, is there any written music, what did it sound like, was it only related to religion or practiced outside religion?
Okay, so maybe a little more than the title.
Having done some cursory research on the topic in response to your question, I will attempt to answer your questions and then suggest some further reading. Please take this as a starting off point, I do not claim to be an expert on this particular topic.
Instruments: We have lots of instruments from ancient Egypt. These include clappers, rattles (meanat), sistrum (kind of like rattles, often sacred to Hathor), cymbals, bells, drums (apparently relatively rare in Egypt), flutes, double vertical flutes/clarinets, oboes, horns (only a few found, probably for military signalling), pan pipes, organs (apparently invented in ptolemaic egypt), harps, lyres, and lutes.
There is no surviving written music, leaving Anderson to speculate that it was never written down and instead passed on orally. Duchesne-Guillemin writes that it was probably heptatonic and modal, based on comparisons with Sumerian and Asian music. She speculates that similar music may still survive among some more remote tribes in Egypt today. It does not appear to have only been associated with religion.
Sources: Duchesne-Guillemin, Marcelle. "Music in Ancient Mesopotamia and Egypt" "World Archaeology" 12.3 (1981) 287-297
Anderson, Robert, reviewer "Music and Musicians in Ancient Egypt" By Lisa Manniche. "Notes" 50.1 (1993) 100-101
Further reading
Lisa Manniche, "Music and Musicians in Ancient Egypt" British Museum Press, 1991.
Anderson, R D "Catalogue of Ancient Egyptian Antiquities in the British Museum 3: Musical Instruments" British Museum Press, 1976