iMac Late 2015: PRAM Reset Chime Sounds Different & Diagnostic's Doesn't Work

Hi there,

So, I have a 27" Late 2015 iMac with the following specs which i configured online:

4.0 Ghz Quad Core i7 (Skylake)

16GB RAM

512GB Flash Storage

M395x 4GB

I decided to do an SMC reset and then a PRAM reset because i was noticing some minor glitches and thats when I noticed an interesting thing I’ve never noticed before with my previous Apple computers (specifically Macbook Pro Retina’s). When I hold CMD + Option + P + R at the same time before the Apple logo, I hear a second chime, but that is it. It then boots straight into the OS. I know the PRAM reset will be fixed after 2 chimes, but technically you can hold the 4 keys to reset the PRAM until however long you want and the boot chime will keep repeating until you let go of those keys. So again, it only does it 2 times and then boots itself into the OS.

Also, the first chime sounds a little bass heavy with lots of lower frequencies coming through from the iMac speaker while the second chime seems like it’s “high pass filtered” or in other words…it sounds mono and as if its coming out of your phone speakers (very weak sounding, no bass, but still loud). This is very weird and it’s never happened before with my Macbook Pro Retina so I’m not really sure if this is something new with the late 2015 5k iMacs.

Now onto another thing I noticed with the Apple diagnostics (I’m going to keep this one short and simple).

• File Vault is inactive
• No firmware password
• I boot up the computer and press D to run Apple diagnostics and it shows a black screen with a small vertical rectangular shape on the top left corner.
• Computer freezes completely and there is no way to boot to the OS from there. I have to force shut down every time.
• Tried running diagnostics by pressing D a few times more after rebooting and the same thing happened.
• Pressing Option + D however actually made the diagnostics work. (Results: No Hardware Issues - but I usually don’t trust the results based on my past experience)
• I've also tried connecting my keyboard and trackpads directly to the computer via USB for both the PRAM reset and the failed diagnostics test

I appreciate any help i can get. This may be a hardware problem or a software problem, I’m not sure. If you think I should return it, let me know, but I would appreciate it greatly if I can also get a proper answer to why this may be happening. I know there are some more experienced people in this community who could maybe tell me what their thoughts are on this issue? I’ve called Apple several times and they all told me to take it in for a refund/exchange.

Thanks!